Question

已知tan(a-b)=1/2,tanb=-1/7求tan(2a-b值

急急急

Answer 1

tana=tan(a-b+b)
=[tan(a-b)+tanb]/[1-tan(a-b)*tanb]
=(1/2-1/7)/(1+1/2*1/7)
=1/3
所以
tan(2a-b)=tan(a+a-b)
=[tana+tan(a-b)]/[1-tana*tan(a-b)]
=(1/3+1/2)/(1-1/3*1/2)
=1