268

tgx-tg3x= tgx -tg(x+2x)=tgx-tgx+tg2x/1-tgx*tg2x=tgx-tgx+2tgx/1-tg²x/1–tgx*2tgx/1-tg²x=

255

ctgα-tgv/ctgv+tgα=cos2α

cosα/sinα-sinα/cosα

cosα/sinα+sinα/cosα=cos²α-sin²α/sinαcosα/cos²α+sin²α/sinαcosα=cosv-sin²α/1 =cos2α