Given that sin theta + cos theta =x, prove that sin^4 theta + cos^4 theta = 2-(x^2-1)^2/ 2

Given that sin theta + cos theta =x, prove that sin^4 theta + cos^4 theta = 2-(x^2-1)^2/ 2

Given that sin theta + cos theta =x, prove that sin^4 theta + cos^4 theta = 2-(x^2-1)^2/ 2