Trigonometric Equations - Double Angle Types (3) | ExamSolutions

[@SupernovaX360A]

These Double Angle videos have been brilliant, thank you. I actually managed to do this question by myself after watching the other 2 worked examples, couldn't of done it without your help.

[@ExamSolutions_Maths]

@PeterJ2k11 sin4θ=cos 2θ. change the sin4θ to 2sin2θcos 2θ using sin2A=2sinAcosA identity where A=2θ So you now have 2sin2θcos 2θ=cos2θ. Subtract cos2θ from both sides to give 2sin2θcos 2θ - cos2θ = 0. Now factorise and get cos2θ(sin2θ - 1) = 0 So now either cos2θ=0 or sin2θ=1 and solve from here.

[@ExamSolutions_Maths]

Thanks for your support

[@PeterJ2k11]

@ExamSolutions Cheers, although I ended up saying let 2θ= x and then working it out then dividing all angles by 2, but i'll definitly try this method, as well the more the merrier haha. Thanks very much again.

[@ExamSolutions_Maths]

Thanks

[@PeterJ2k11]

@ExamSolutions Cheers, although I ended up saying let 2θ= x and then working it out then dividing all angles by 2, but i'll definitly try this method, as well the more the merrier haha. Thanks very much again. I've just realised that was the exact same thing you have done, and I had misread your reponse, due to mathmatical fatigue haha, tragic times, cheers though.

[@Benedictninja]

hey! why at 3:00 can't you divide the 3tanx on both sides, so you get 1-tan^2 x= 2/3 ? many thanks anyway!

[@ExamSolutions_Maths]

If I did that I would divide out a factor which is a solution and hence loose it. i.e. tan x = 0. Common mistake.

[@mazedulchowdhury483]

Great Explanation, Sir.

[@ExamSolutions_Maths]

Thank you.

[@vishalpanesar23]

Hi sir i was wondering why isnt is possible to do 2tanx/3tanx = 1-tan^2x the + or - 1/3 is obtained however the zero is not why would this be??

[@PeterJ2k11]

This has been really helpful thank you. However, I was having difficulties in solving trig question when it is more than a double angle e.g. the question sin4θ=cos 2θ. Here would you split up sin 4θ into sin(2θ+2θ)? I'm honestly not sure, thank you in advance.

[@GreenTornado]

Is it possible (and allowed in an exam) to use just your calculator and your knowledge of the unit circle when finding the solutions to trigonometric equations? I hate sketching graphs. It is time consuming, too, if multiple graphs have to be sketched.

[@hamayun24]

Can you please solve Cos2x = Sin 3x ?

[@ionaf9]

at 11:25 you wrote 11/6 instead of 11π/6 tiny mistake but I hope don't do that in the exam!!

[@ExamSolutions_Maths]

+DefoNotObsessed Oops!

[@flawns]

wow this is a year ago, but maybe if you are still intrested??? cos2x= cos(x+x) Distribute = cos(x)cos(x) - sin(x)sin(x) = cos²(x) - sin²(x) same thing is done with sine3x but sine(2x+x)

[@3ej6]

you have a nice voice