ctg 2α = (ctg²α - 1)/2ctgα
ctg α = cosα/sinα = cosα/√1-cos²α = (-3/5)/√1-9/25 = (-3/5)/(4/5)= -3/4
ctg 2α = ((-3/4)²-1)/2(-3/4) = -7/16*(-6/4) = 42/64 = 21/32
ctga=cosa/sina=cosa/√1-cos²a=(-3/5)/√(1-9/25)=(-3/5)/(4/5)=(-3/5)*5/4=-3/4;
ctg2a=(ctg²a-1)/2ctga=((-3/4)²-1)/2(-3/4)=-7/16*(-6/4)=42/64=21/32.
ctg 2α = (ctg²α - 1)/2ctgα
ctg α = cosα/sinα = cosα/√1-cos²α = (-3/5)/√1-9/25 = (-3/5)/(4/5)= -3/4
ctg 2α = ((-3/4)²-1)/2(-3/4) = -7/16*(-6/4) = 42/64 = 21/32
ctga=cosa/sina=cosa/√1-cos²a=(-3/5)/√(1-9/25)=(-3/5)/(4/5)=(-3/5)*5/4=-3/4;
ctg2a=(ctg²a-1)/2ctga=((-3/4)²-1)/2(-3/4)=-7/16*(-6/4)=42/64=21/32.