已知tanα=2,求 3sin²α+3sinαcosα-2cos²α

已知tanα=2,求 3sin²α+3sinαcosα-2cos²α
已知tanα=2,求 3sin²α+3sinαcosα-2cos²α

已知tanα=2,求 3sin²α+3sinαcosα-2cos²α
3(sinα)^2+3sinαcosα-2(cosα)^2
=[3(sinα)^2+3sinαcosα-2(cosα)^2]/[(sinα)^2+(cosα)^2] 分子分母同除(cosα)^2
=[3(tanα)^2+3tanα-2]/[(tanα)^2+!]
=(3*4+3*2-2)/(4+1)
=16/5

16/5

见图