若3sina+cosa=0,则1/sin^2a+cos^2a= A.10/3 B.5/3 C.2/3 D.-2
问题描述:
若3sina+cosa=0,则1/sin^2a+cos^2a= A.10/3 B.5/3 C.2/3 D.-2
答
3sinA+cosA = 0
tanA = -1/3
(sinA)^2 = 1/10
(cosA)^2 = 9/10
1/(sinA)^2 + (cosA)^2
= 10+9/10
=109/10