(1),r^2=x^+y^2=5+20=25,r=5.角θ的终边经过P（√5,2√5）,所以角θ是第一象限的角,故sinθ=y/r=2√5/5,cosθ=x/r=√5/5.(2),sin(θ-φ）＝√10/10,0＜θ-φ＜π/2,则：(cos(θ-φ))^2=1-(sin(θ-φ))^2=1-1/10=9/10...