己知tan=3.求sin-2cos分之3sin-cos

己知tan=3.求sin-2cos分之3sin-cos
己知tan=3.求sin-2cos分之3sin-cos

己知tan=3.求sin-2cos分之3sin-cos
tanα=sinα/cosα=3
sinα=3cosα
(3sinα-cosα)/(sinα-2cosα)
=(9cosα-cosα)/(3cosα-2cosα)
=8cosα/cosα
=8

tan=sin/cos=3 得sin=3cos
代入得 (3cos-2cos)/(9cos-cos)=1/8