Question

siendo: secx=8senx. calcular: cos4x​

Answer 1

1/cosx = 8senx

1/4= 2senxcosx

sen2x=1/4 ==> cos2x=√15/4

cos4x=(cos2x)^2-(sen2x)^2

=(√15/4)^2-(1/4)^2

=15/16-1/16=14/16

cos4x=7/8