Question

1.已知tan x=负2,则1/4sin x 平方+2/5cos x的平方=?

Answer 1

tan x=-2=sinx/cosx

sinx^2/cosx^2=4

sinx^2=4cosx^2

sinx^2+cosx^2=1

所以

sinx^=4/5,

cosx^2=1/5

1/4sin x 平方+2/5cos x的平方

=1/4*4/5+2/5*1/5

=7/25