268

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

278

1/1+tang²d+1/1+crg²d=1

1/1+sin²α/cos²α+1/1+cos²α/sin²α=1/cos²α+sin²α/cos²α+1/sin²α+cos²α/sin²α=cos²α/1+sin²α/1=1

276

cos²(π+α)+cos²(π/2+α)=1

1=1

277

(1+ctg²α)(1-sin²α)=ctg²α

(1+cos²α/sin²α)cos²α=ctg²α

sin²α+cosv/sinv*cos²α=ctg²α

cos²α=ctg²α

ctg²α=ctg²α

255

ctgα-tgv/ctgv+tgα=cos2α

cosα/sinα-sinα/cosα

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