Question

verify the identify cos(2A)=1-2sin^2(A) using Cos (A+B)=cosA CosB- SinA SinB

Answer 1

\[\cos2A=\cos(A+A)\]

Answer 2

can u do it further??

Answer 3

expand it

Answer 4

cosA*cosA-sinA*sinA

Answer 5

cos^2A-sin^2A

Answer 6

cos^2A=1-sin^2A

Answer 7

plug it in place of cos^2A

Answer 8

you lost me at cosA*cosA-sinA*sinA

Answer 9

sum of angles identity is cos (A+B) =cosAcosB-sinAsinB
in this case B=A so just sub it in gurl

Answer 10

cos(A+A)=cos ^2 A-sin ^2 A=1-2sin ^2 A since, sin ^2 A+ cos ^2 A=1

Answer 11

@sierralake