Question

求Y= 1/(COSX的平方) + 2/(SINX的平方) (X为锐角)的最小植

Answer 1

(sinx)^2+(cosx)^2=1代入,化简,y=1+(sinx)^2/(cosx)^2+2+(cosx)^2/(sinx)^2=3+(tanx)^2+(cotx)^2>=3+2根((tanx)^2*(cotx)^2)=5,x=45度取最小值.