设tan a = 1/2 ,tan b =1/3 ,则cot (a +2b )

问题描述:

设tan a = 1/2 ,tan b =1/3 ,则cot (a +2b )

tan b =1/3
tna2b=2tanb/(1-tan²b)=2/3÷(1-1/9)=3/4
tan(a+2b)=(tana+tan2b)/(1-tanatanb)
=(1/2+3/4)÷(1-3/8)
=7/5
所以,cot(a+2b)=1/tan(a+2b)=7/5