Question

已知cot a=2,求(sin^2 a-3cos^2 a)/(2sin^2 a+cos^2 a)的值

Answer 1

(sin^2 a-3cos^2 a)/(2sin^2 a+cos^2 a)

（同时除以sin^2 a）

=(1-3cot^2 a)/(2+cot^2 a)

=(1-3*4)/(2+4)

=-11/6