Question

tan(A+B) = (tanA+tanB) / (1-tanA * tanB) = -1从而得到:tanA+tanB

Answer 1

(tanA+tanB) / (1-tanA * tanB) = -1

两边同乘以 (1-tanA * tanB),等式两边就为

(tanA+tanB)= - (1-tanA * tanB),“-“(1-tanA * tanB)注意这个外面有一个负号打开括号后

(tanA+tanB)= - (1-tanA * tanB)=tanA * tanB-1