cosa*sinb=-1,cos(a+b)=多少
问题描述：
cosa*sinb=-1,cos(a+b)=多少
A.0 B.1 C.-1 D.1或者-1
答
∵-1≤cosa≤1,-1≤sinb≤1又∵cosa*sinb=-1∴cosa=-1,sinb=1或cosa=1,sinb=-1①cosa=-1,sinb=1则a=π+2kπb=π/2+2kπk∈Z∴cos(a+b)=cos(3π/2+4kπ)=0②cosa=1,sinb=-1则a=2kπb=-π/2+2kπk∈Z...