sin^4x-cos^4x /sin^2x-cos^2x=1 Let theta =xSir proof this equation .This question is in exercise 7.1 of 10 class book of rbse.

You can write Sin^4θ - cos^4θ as (sin^2θ + cos^2θ)(sin^2θ - cos^2θ) by applying simple formula that is a^2 - b^2 =(a+b)(a-b). Now (sin^2θ + cos^2θ)(sin^2θ - cos^2θ)/(sin^2θ - cos^2θ) = sin^2θ + cos^2θ =1.