Question

find all solutions
7 sin2x - 14 sin x + 2 = -5

Answer 1

is that sin^2 x - the square of sine x?

Answer 2

just you need note sinx = y and will get a quadratic in y what you can solve it sure - ok. ?

Answer 3

The best way to solve this is to say that:

sin x = y

And if you replace your equation with that, you get

7y^2 - 14y + 2 = -5

First set it equal to 0, and then solve the quadratic function for y.

After that, we'll solve the rest of your problem. :)