Respuesta :

ramashshrestha92

cos4A-sin4A=2cos2A-1

proved below.

Step-by-step explanation:

Given:

cos^4A-sin^4A=2cos^2A-1

LHS=cos^4A-sin^4A

=[cos^2A]^2-[sin^2A]^2

=[cos^2A+sin^2A][cos^2A-sin^2A]

=[1][cos^2A-(1-cos^2A)] [ cos^2A+sin^2A=1]

=[cos^2A-1+cos^2A]

=2cos^2A-1

=RHS.