tan(a b)=3,tan(a-b)=5.則tan2a的值是多少？

熱心網(wǎng)友

tan(a b)=3,tan(a-b)=5.則tan2a=tan[(a +b)+(a-b)]=[tan(a +b)+tan(a-b)]/(1-tan(a +b).tan(a-b))=-4/7