brilliant geometry problem

[@caperider1160]

Alternatively, you can draw a perpendicular line from A to meet BC to set up the equation using Pythagoras theorem now that the two right angled triangles have common height. Those who talk of cosine rule doesn't appreciate the beauty of maths, imo.

[@vishalmishra3046]

Using *cosine rule* cos A = (3^2 + 5^2 - 7^2) / (2 x 3 x 5) = (9 + 25 - 49 = -15) / (2 x 15) = -1 / 2 = cos 120 (since 49 > 9 + 25 an obtuse angle was anyway expected). So, A = 120 deg.

[@respawn.3d]

nice vid keep up

[@krishnachoubey8648]

Excellent video man 😊 👍

[@PrithwirajSen-nj6qq]

There is no necessity to find the measure of angle CAD Angle BAC =Angle ACD + angle ADC = 30 +90=120 degrees

[@ManjeetRani-v5n]

just use law of cosine

[@mykolatyshchenko8987]

Coulda just used the law os cosines)

[@krishnachoubey8648]

But elementary proof are nice😊