Question

已知tanx=2运用三角万能置换公式求sin2x.cos2x.tan2x

Answer 1

由万能公式,

sin2x=（2tanx)/[1+(tanx)^2]

=2*2 / 12*2

=4/5

cos2x=[1-(tanx)^2]/[1+(tanx)^2]

=(1-2*2)/(1+2*2)

=-3/5

tan2x=（2tanx)/[1-(tanx)^2]

=(2*2)/(1-2*2)

=-3/4