Question

tanx=2 求sin^2x+sinxcosx-3cos^2x

Answer 1

tanx=2

sinx/cosx=2

sinx=2cosx

(sinx)^2+(cosx)^2=5(cosx)^2=1

(cosx)^2=1/5

(sinx)^2+sinxcosx-3(cosx)^2

=(cosx)^2(4+2-3)

=3(cosx)^2

=3/5