(1)当a//b时,求tanx的值sinx/1=cosx/1tanx=1(2)若f(x)=a乘b,f=sinx+cosx=根号2sin(x+45)单调递增区2kπ-π/2 <=x+π/4<=2kπ+π/2 2kπ-3π/4 <=x<=2kπ+π/4