已知a,b为锐角,cosa=4/5,tan(a-b)=-1/3,求cosb的值

Question

已知a,b为锐角,cosa=4/5,tan(a-b)=-1/3,求cosb的值

Answer 1

cos a =4/5 所以sin a =3/5 所以tan a =3/4;
tan(a-b)=(tan(a)-tan(b))/(1+tan(a) * tan(b)) =>tan b =13/9
又b是锐角 所以 cos b =9/16
楼主给分哈