26.10б
sint*cost/(-tgt)*(-cost)=sint:sint/cost=sint*cost/sint=cost
26.10г
(-sint)*sint/tgt*sint=-sint:sint/cost=-sint*cost/sint=-cost
26.11a
(-cost+sint)/(-sint+cost)=-1
26.12б
(-cosx)*(-ctgy)/(-cosx)*tgy - (-cosy)*(-tgx)/cosy*(-tgx)=-ctgy/tgy+1=
-ctgy:1/ctgy +1=-ctg²y+1