Digital SAT Prep: Easy Desmos Hack for the Hardest Math Problems!

[@savvas637]

Another very easy solution for question 2 I think would be to know that the Product = c / a so because c = ab and a = 57 , c/a = ab/57 = kab . The ab’s cancel out and we’re left with 1/57 = k

[@harshithgogineni7093]

would've never thought of this. wow!

[@armaan7381]

vietta's formula

[@emmazhang2418]

why is a 57?

[@savvas637]

@@emmazhang2418Because the formula for a quadratic equation is: ax^2 + bx +c = 0 so by comparing this to the equation given in the question a is 57

[@vivianlee2509]

how do you know that c=ab ?

[@chadchampion7985]

Here's an alternative solution to the last problem: a+b+c is f(1). Since the parabola is open upwards, (9, -14) is the minimum value of f(x). Thus, f(1) (whatever it is) must be greater than 14 i.e. a+b+c > -14 Only choice d fulfills this criteria.

[@derinwithaq5811]

that's actually very helpful, and much better than her very not rigorous "well it's probably mostly positive" explanation

[@abdullah_abisola]

That is mad I am blown away by this method I happened to try this on my own and landed at College Board's explanation but I also thought of this Cause Ik that 2a = 2nd diff 3a +b = 1st diff and a + b + c = 1st Term Thanks Alot

[@psych0-shorts]

Dude I was trying to look for a proof that a+b+c = f(1) for like 10 mins. Then I just plugged in a 1… I felt so stupid bro LMFAO

[@bexqmish3699]

Took me a sec to understand it, but that's really clever

[@shlattrt]

@@bexqmish3699 bro I don't get it can u help

[@ucheshub23]

You saved my Nigerian Life😩. I could kiss you. Thank you so much Ma'am. ♥️♥️✌️✌️

[@meadowxchannel]

Shes about to save mine too

[@stays4514]

​@@meadowxchannelyou're a Nigerian taking the sat this Saturday??

[@NamGil-ed5bf]

@@stays4514yes

[@lasfd6606]

what did u get

[@adityabhambhani207]

This right here is a goldmine!! Thanksss! rlly helpful!!

[@gregnixon1296]

Becoming a calculator jockey is an under-rated strategy. A TI-84 Plus CE has functions in the APPS menu that bring high scores well within reach. You don’t need to be a math guru, just understand how to use the allowed tools.

[@letsgotousa679]

Please make a video on "hard reading questions" on module 2

[@meadowxchannel]

This was so helpful, thanks so much!

[@KonradTittel]

A shortcut for the second problem is to have the what's called "Vieta's Formula's" memorized, which are really simple: the product of the solutions (roots) of a quadratic ax^2 + bx + c is c/a, and the sum of the roots is -b :D

[@reonmel8523]

sum of solutions is -b/a

[@leonmaurice1746]

I solved these problems like this: 92) Use Discriminant D=0; b^2-4ac = 0. Solving for a gives a = 14.5 95) Use x1*x2 = c/a = ab/57; k= 1/57. 98) V(9/-14); f(x) = a(x-9)^2 - 14 = ax^2 - 18ax + 81a - 14; a+b+c = 64a - 14. Since the parabola touches the x-axis twice and yV = -14, the limit as n->∞ is ∞, and, thus, a>0, from which follows that 64a - 14 > -14. The solution, hence, must be -12.

[@azretomarrisbay8925]

Hi can i ask how did you get 64a-14?

[@leonmaurice1746]

@@azretomarrisbay8925 Admittedly, my notation was plain wrong there, sorry about that. I should have written a new equation after f(x) = ax^2 -18ax +81a -14. The polynomial equality theorem for polynomials says that if two polynomials are equal to each other for all x∈𝔻, that the coefficients cn of each degree n of x, where n∈ℕ0, have to be equal as well (you don't really need to know this theorem, it's intuitive that the coefficients must be equal). We know that f(x)=ax^2 + bx + c and we derived that f(x)=ax^2 -18ax + 81a - 14 using the vertex form. The vertex and standard form are equivalent, so that ax^2 + bx + c = ax^2 -18ax + 81a -14. Now apply the polynomial equality theorem, from which follows that a=a, b=18a, c=81a-14. It immediately follows that a+b+c= 64a -14. The parabola is open upwards (you realize this when visualizing the vertex below the x-axis and the fact the graph touches the x-axis twice, the limit was a mere notational formality), so a>0. Thus, 64a-14 can never be smaller than -14. We, hence, get (D) -12 as our only option.

[@azretomarrisbay8925]

@@leonmaurice1746 my bad, i missed the a+b+c part you wrote and thought u just got ax^2-18ax+81a-14=64a-14, now its clear thx for explanation🙏

[@leonmaurice1746]

@@azretomarrisbay8925 you're welcome (and were right though btw, I did have it like that before, I corrected it after you commented)

[@dundundun2383]

thank you for 98 because i also got 64a-14 but didnt know where to go from there

[@montysark]

If you know a little bit of calculus, you don't even need desmos. y = -1.5 y = x^2 + 8x + a you can find the derivative of the second equation then set that equal to 0. then solve for x and that will give you the critical point. then insert that solution into x^2 + 8x + a = -1.5 then solve for a . and you've got it.

[@StrategicTestPrep]

Love this!! Very cool

[@rotimifr]

yes. well explained really helpful if you know how to get the derivative.

[@dkdebbie1398]

Helped me raise my math score by 150 point 🙏🙏🙏🙏

[@lunalinedigital_1733]

8:36 I don't get why D is the answer. What if c was less than a and b, wouldn't that make a + b + c answer as positive?

[@YTAlyx]

Her answer is right, but the method is not. Instead what you can do is write the equation in the form of a(x+b/2a)^2 + c - a*(b/2a)^2 (Squared form to find the vertex) and you have the values where b/2a=-9 And c - a*(b/2a)^2 = -14 Now find b and c in terms of a Substitute in a + b + c to get an equation in a You will get 64a-14 = ... To get a +ve value for "a". The ... (which is the answer) has to be lesser than 14, since they are all -ve values. Hence D is the answer

[@angelinatayar7873]

practice test 6 math harder module last 5 questions can u do them please using desmos

[@lexi_virtual_diary]

Thank u sooooo much ...u hv no idea how this really helped..

[@Ela-gv7tr]

usa maths is crazy, they're not testing your actual mathematical abilities at all, all of these questions are stupidly easy, they're just testing speed/ tricks atp

[@SayfuddinQambarov]

I can relate this , you are an Asian like me ?😅😅

[@rohey.3285]

exactly it’s just to see if you understand the concept

[@Ela-gv7tr]

@@SayfuddinQambarov haha no I’m from the UK and I’ve done A level maths

[@nahomdesta1237]

Thank you for what you do to help us, Laura. I've been watching your videos for a while now and I really appreciate what you do. But, I have a question on the second question. Why exactly did we set a and b as 1?

[@StrategicTestPrep]

Great question - They’re just easier numbers to work with! You could set a and b as anything. And thank you I appreciate you watching 😊

[@raquele.1025]

@@StrategicTestPrepHi! I tried putting in b=5 and a= 5 to see if your method would still work for numbers other than 1, but I didn't get the same solution. I also double checked to make sure that my equation was correct. Any advice?

[@starfish2884]

​@@raquele.1025 I think I figured it out. When you put b=5 and a=5, the product of the solutions is 0.4386. Since the product of the solutions is kab, you have to dived 0.4386 by ab which is 25. Then you will get 0.17544.

[@mathwithmelissarose]

Great tips! Thanks for sharing

[@StrategicTestPrep]

Aw you’re welcome, Melissa!

[@fredabila]

Your explanation for using the calculator was easy to comprehend but the solution to the questions were quite difficult to understand

[@AlizeyJahanzeb]

I have a question for the sliders how do you know what number to put like for the question where both a and b were one how do you know it has to be one

[@sync213]

I think you can put any number in those, it would change the x-intercepts but once you solve again with the new x-intercepts, you wil still get .018. 1 was just a easy number to solve the k*a*b equation with, but any number should work if you solve it right.

[@AlizeyJahanzeb]

@@sync213 thank you😀

[@shehlabtskz]

Thank you so much teacher it was so helpful to me❤. We are waiting for the part 2

[@psych0-shorts]

The first one isn’t that bad really. If it says that it only has one solution then it means that the lines only hit once. For that to happen y=-1.5 (the straight line) has to be just touching the bottom part of the parabola (height at vertex). We know that the vertex is x= -b/2a, and height y = f(-b/2a). From there its making the line’s height = to the vertex height.

[@ValentinaRubio-g9d]

for the last question would it also work if I add the minimum plus the x intercept plus the y intercept? It also gives 12 but I don't know if that is a correct way to solve.

[@parrotsarecolorful01434]

oh my god the lighting how many lights do you have haha nevertheless, you always drop banger videos.

[@StrategicTestPrep]

💙🙏💙

[@MasterrHalal]

I have my exams on Oct 7 🥹 And I am currently hitting only 640 in Maths and 630 in English .I need to improve at least 80 points each in the next 27 days 🙂 Totally scared

[@ucheshub23]

Seriously 😢.

[@MasterrHalal]

@@ucheshub23 Promise brother 🥲 I wish I had started earlier

[@khanhcatbi]

Hows it going now bro

[@delightfulgenius4635]

What did you get up to?

[@invisisense5464]

How was it?

[@McKylie151]

can we use Desmos during the exam?

[@duck-vt4co]

It's on the test!

[@McKylie151]

@@duck-vt4co ohh I see thank you♡

[@StrategicTestPrep]

Yea you can!

[@dougd120]

Another was the day of things.

[@denji3017]

can desmos be used on two sections?

[@LUIZcomZ-0]

yes

[@euniceolaoye2146]

Hey, i have never used the desmos and my exam is on saturday. Do you advise that i should just stick with using my calculator or get familiar with the desmos?

[@allisonturner5571]

Hi random person, how did it end up going? In the same situation I'm wondering if the best is to use desmos as a last resort if I have no idea what to do.

[@unbalancedbee]

@@allisonturner5571hi i saw some tutorials on how to use desmos for dsat! if you’re taking the august exam i suggest you to watch them, they’re very helpfullll! (Edit: the videos are so short and easy to understand so watching them may help since there is a short period of time left)

[@elcinseydayev4904]

why we give same number to a and b at question 95.They are actually not the same thing

[@amena4887]

i have the same question !! im so confused

[@freakyrein]

I'm a 10th grader and I'm going to pass my SAT test in March, but I haven't studied most of the math problems in there yet. I don't know what to do 💀

[@robzombies]

I know this is from two weeks ago but it's never too late to study! Start taking notes and practice, do memory training methods to see how much you remember for the SAT, You've got this!

[@milky1l896]

The explanations for math problems on the SAT are the same since the paper SAT so they don't use desmos at all 😭

[@mollygarnett5685]

Why is it a(x-9) for Practice 4, question 98?

[@rodrigue9228]

This is the canonic form of the equation : y = a(x-A)^2+B where A and B are the x and y coordinate of the vertex.

[@orange_turtle3412]

Giving testers free access to desmos was the biggest mistake college board ever made. Hehehe…

[@Dawodu_Gbolahan_David]

Please I want to buy your course but is only English I want to buy because I can't afford both with the price given but I really want to buy the English

[@soichchha_]

When will the sat score will publish? Of August 26 Digital

[@obadaalibek732]

8th september after two days

[@dhiraj7b1vallabhaneni30]

could u do the hardest english questions?

[@thx1136]

... with Desmos

[@linhnhi4142]

but do the desmos on bluebook has a slider? i've done all of the practice tests but never notice there's a slider

[@StrategicTestPrep]

There absolutely is a slider when you input a variable other than x or y

[@leul_me]

not trying to hate but you should stick to your eng the last explanation was just so confusing Also it is much easier to do the question in this example by your own ure gonna save a lot of time

[@lawrencewilson832]

Actually, if you read the answer given by the College Board it isn't that complicated. They're just saying that the discriminant has to be zero if there is one real solution. I think setting the discriminant equal to zero and solving for a is much quicker and easier than what you're suggesting. Plus knowing how the discriminant relates to zeroes of a quadratic equation can help with other types of these questions on the SAT. Your method doesn't.

[@thetechsolutions4420]

Hardest 😂

[@Medmew-j1u]

Are y'all dump in America? That algebraic solutions are literally what every modern freshman in Kazakhstan would be shameful of not knowing. And it's Kazakhstan, man. Can't imagine what the Russian or Chinese students thinking about this.

[@m.3tamorphos1s]

nga said dump

[@tacotanger5125]

😭 name one college in the top 100 in kazakhstan or any noble prize winners💀

[@Medmew-j1u]

@@tacotanger5125 that's the point. We don't have those and yet we can solve these math problems.

[@tacotanger5125]

@@Medmew-j1u wtf did kazakhstan even contribute to the world😭

[@Medmew-j1u]

@@tacotanger5125 is that the main issue or I offended u so badly u gotta say smth about my country 😂

[@RiverieEssence]

she keeps yapping so much.. such a time waste

[@NneomaIjeoma]

Laura thank you so much for all your videos. You aren't just smart, you're also super pretty 🥹

[@StrategicTestPrep]

Awwwww thank you so much!! 🥰