已知(1-tana)/(2+tana)=1

问题描述:

已知(1-tana)/(2+tana)=1
求证tan2a=-4tan(a+派/4)

1-tanA/2+tanA=11-tanA=2+tanA tanA=-1/2; tan2A=2tanA/(1-tan^2 A)=2*(-1/2)/[1-(-1/2)^2]=-1/[1-1/4]=-1/(3/4)=-4/3 -4tan(A+π/4)=-4*[(tanA+tanπ/4)/(1-tanAtanπ/4)]=-4*[(tanA+1)/(1-tanA)]=-4*[(-1/2+1)/(...