cosy×sinx=2/3
求cosx×siny的范围
cosy×sinx=2/3
求cosx×siny的范围
由三角恒等变换知识:
cosysinx+cosxsiny=√2sin(45°+x+y)
∴cosysinx+cosxsiny的取值范围为[-√2,√2]
又∵cosysinx=2/3
∴cosxsiny的范围为[-√2-2/3,√2-2/3]
-1≤cosx×siny+cosy×sinx=sin(x+y)≤1,-1-2/3≤cosx×siny≤1-2/3
-5/3≤cosx×siny≤1/3