tan0.5°=0.0087tan1°=0.0175tan2°=0.0349tan3°=0.0524tan4°=0.0699tan5°=0.0875tan10°=0.1763tan20°=0.3640tan50°=1.1918
律乘以abb(b+x)=a(x-a)b2+bx=ax-a2(a-b)x=a2+b2所以a=b=0,有无数解a=b≠0,无解a≠b,x=(a2+b2)/(a-b)
