Question

tana=-1／2则sin2a+2cos2a／4cos2a-4sin2a的值是?

Answer 1

tana=-1／2

故tan2a=2tana/[1-(tana)^2]=2×(-1/2)/[1-(-1/2)^2]=-4/3

则

(sin2a+2cos2a)／(4cos2a-4sin2a) 分子分母同除以cos2a

=(tan2a+2)／(4-4tan2a)

=(-4/3+2)／[4-4×(-4/3)]

=1/14