How do you solve 2 cos squared x - sinx - 1?

Answer 1

1

Answer 2

Remember the Trig. Identity

Cos^(2)x = 1 - Sin^(2) x

Hence substitute

2(1 -Sin^(2)x )- Sin(x) - 1 = 0

2 - 2Sin^(2)X - SinX - 1 = 0

-2Sin^(2) - SinX + 1 = 0

2Sin^(2)X + SinX - 1 = 0

It is now in quadratic form ; Factor !!!!

(2SinX - 1)(SinX + 1) = 0

2SinX - 1 = 0

SinX = 1/2 = 0.5

X = 30 , 150, 390, 690,....

&

SinX + 1 = 0

SinX = -1

X = 270, 630,

Answer 3

Sin2x + Cos2x =1

You can rearrange this to say: Cos2x = 1 - Sin2x

Put this in place of Cos2x in the original equation and it should be easier :)