设向量A=(4COSX,SINX),向量B=(SINY,4COSY);向量C=(COSY,-4SINY) (1)若A与B-2C垂直,求TAN(X+Y)的值(2)B+C的绝对值的最大值(3)若TANXTANY=16,求证:A平行B_百度作业帮
设向量A=(4COSX,SINX),向量B=(SINY,4COSY);向量C=(COSY,-4SINY) (1)若A与B-2C垂直,求TAN(X+Y)的值(2)B+C的绝对值的最大值(3)若TANXTANY=16,求证:A平行B
⑴ A·(B-2C)=4sin(x+y)-8cos(x+y)=0.
tan(x+y)=2⑵
|B+C|²=17-16sin2y,
|B+C|的最大值=√33.⑶
TANXTANY=16,sinxsiny=16cosxcosy,4cosx/sinx=siny/4cosy,A‖B
B-2C=(SINY-2COSY,4COSY+8SINY)所以A*(B-2C)=4COSX(SINY-2COSY)+SINX(4COSY+8SINY)
=4COSXSINY-8COSCOSY+4SINXCOSY+8SINXSINY
=4SIN(X+Y)-8COS(X+Y)A垂直B-2C即有A*(B-2C)=0