Question

若2sinx ＋cosx＝0,则1/（sin∧2x-cos2x）等于?

Answer 1

2sinx ＋cosx＝0,2sinx=-cosx ,4sin^2x=cos^2x=1-sin^2x,sin^2x=1/5

1/（sin^2x-cos2x）=1/[sin^2x-(1-2sin^2x)]

=1/(3sin^2x-1)

=-5/2