sin²α+cos²α=1所以sin²α+4sin²α=1sin²α=1/5sinα=±√5/5cosα=2sinα=±2√5/5tanα=sinα/cosαcotα=1/tanαsecα=1/cosαcscα=1/sinα所以sinα=√5/5cosα=2√5/5tanα=1/2cot...