Question

3 cos ^ 2 theta - 5 cos theta - 1 - 3 sin ^ 2 theta = 0

3 cos ^ 2 theta - 5 cos theta - 1 - 3 ( 1 - cos ^ 2 theta ) = 0

3 cos ^ 2 theta - 5 cos theta - 1 - 3 + 3 cos ^ 2 theta = 0

6 cos ^ 2 theta - 5 cos theta - 4 = 0

Substitute :

u = cos theta

6 u ^ 2 - 5 u - 4 = 0

The exact solutons are :


u = cos teta = 4 / 3 = 1.333

and

u = cos theta = - 1 / 2


cosine can't be great of 1

so the solutions are :

cos theta = - 1 / 2


theta = ( 2 / 3 ) pi = 120 �

and

theta = ( 4 / 3 ) pi = 240

Answer 1

looks correct to me

Answer 2

thanx!

Answer 3

@lgbasallote can u find the ans of this^^

Answer 4

seems right to me too...