Differentiate (cos θ - sin θ)\(^2\)

Craig Duffy

9 years ago

let cos© be x

let sin© be y



(x - y)^2



= x^2 - 2xy + y^2



= (x^2 + y^2) - 2xy



that is ;cos^2© + sin^2© = 1

= 1- 2xy



den u differentiate

d derivative of 1= 0

and d derivative of 2cos©sin© = 2cos^2 - sin^2



= 0 - 2 cos^2 - sin^2

= - 2cos2©



if u re a bit confused abt how ah got the final answer.. den, u had better go and study COMPOUND ANGLES AND BASIC IDENTITIES .

Craig Duffy

9 years ago

my school got d penultimate of their solution wrong... CUs,if dy re to express , cos^2© -,sin^2© in terms of sin^2©, den, it shud be , 1 - 2sin^2© (which is also equals cos2©) and not {1-sin^2©.}

Futureqween3

9 years ago

thanks