已知3cos(2X+B)+5cosB=0,则tan(X+B)乘以tanX的值为有四个选项A.+_4 B.4 C._4 D.1_数学解答

已知3cos(2X+B)+5cosB=0,则tan(X+B)乘以tanX的值为
有四个选项A.+_4 B.4 C._4 D.1

人气：404 ℃　时间：2020-04-13 08:32:58

解答

3cos(2X+B)+5cosB=0
3cos(X+B+X)+5cos(X+B-X)=0
3cos(X+B)cosX-3sin(X+B)sinx+5cos(X+B)cosX+5sin(X+B)sinx=0
8cos(X+B)cosX=-2sin(X+B)sinx
-4=sin(X+B)sinx/cos(X+B)cosX
tan(X+B)tanX=-4
选C