Question

4sin^4 θ + 3sin^(2) θ-1=0

Answer 1

let sin^2 theta=x
so the problem reduces to,
4x^2+3x-1=0
so solving by middle term factor method,
(4x-1)(x+1)=0
so,
x= 1/4 as the other is not possible.
so sin theta=sqrt(1/4)=(+,-)(1/2)

Answer 2

do you understand the steps?