Question

Cos(20°)-sin(20°)=p then cos(40°)=

Answer 1

Hey mate,

cos 20 - sin 20=p

square it

cos220 + sin220 -2sin20cos20 =p2

sin40 =1-p2

and cos40 =(1-sin240)1/2

=(2p2-p4)1/2

Hope it will help you.