设a=2tsint=√(sin^2t+cos^2t+2sintcost)-√(sin^2t+cos^2t-2sintcost)sint=|sint+cost|-|sint-cost|sint=±2sint或±2costsint=0,cost=±1,等式成立tant=0,tana=0sint=±2costtant=±2tana=2tant/(1-tan^2t)=±4/3...