若sin^2+sina=1,则cos^4a+cos^2a=——

若sin^2+sina=1,则cos^4a+cos^2a=——
若sin^2+sina=1,则cos^4a+cos^2a=——

若sin^2+sina=1,则cos^4a+cos^2a=——
sin²a=-sina+1
所以cos²a=1-sin²a=sina
原式=sin²a+sina=1

若sin^2a+sina=1,
得sina=1-sin^2a=cos^2a.
cos^4a+cos^2a
=cos^2a(cos^2a+1)
=sina(sina+1)
=sin^2a+sina
=1-sina+sina
=1