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