Question

tan65+tan70-tan65*tan70=?

Answer 1

因为tan 135 = tan(65 + 70) = (tan65 + tan70)/(1- (tan65 * tan70)) 而tan 135 = -1 则-1=（tan65 + tan70)/(1-(tan65 * tan70)) -(1-(tan65 * tan70))=tan65 + tan70 tan65 + tan70 + 1 -(tan65 * tan70)=0 tan65...