问题5:如图,单位圆中,假设点P1的坐标为(x,y),你能说出P2的坐标吗?

　　请用三角函数的定义写出角π/2-α的三角函数(诱导公式五):{■(sin"(" π/2 "-" α")" =@cos"(" π/2 "-" α")" =)┤

　　2.诱导公式六:

　　思考:同学们,角π/2+α与角α又有怎样的关系呢?你仍然是画图研究,还是用已学的公式来探究呢?请试着写出你推导诱导公式六的过程.

　　得到公式六:{■(sin"(" π/2+α")" =@cos"(" π/2+α")" =)┤

　　观察可得记忆口诀:

　　二、课堂完成部分

　　(一)典型例题

　　【例1】化简下列各式:

　　(1)(sin"(" π/2+α")" cos"(" π/2 "-" α")" )/(cos"(" π+α")" )+(sin"(" π"-" α")" cos"(" π/2+α")" )/(sin"(" π+α")" );

　　(2)(sin^3 "(" π/2+α")" +cos^3 "(" π/2+α")" )/(sin"(" 3π+α")" +cos"(" 4π"-" α")" )-sin(5π/2+α)cos(3π/2+α).

　　【例2】化简(sin"(" α+nπ")" +sin"(" α"-" nπ")" )/(sin"(" α+nπ")" cos"(" α"-" nπ")" )(n∈Z).

　　【例3】(1)已知tanα=3,求值:(2cos"(" π"-" α")-" 3sin"(" π+α")" )/(4cos"(-" α")" +sin"(" 2π"-" α")" );

　　(2)已知(sinα+cosα)/(sinα"-" cosα)=3,求(sin^2 "(" 2π"-" α")" +2sinαcosα)/(tan"(" π+α")(" 1+sin^2 α")" )的值;

(3)求值√(1"-" 2sin100"°" cos100"°" )/(cos350"°-" √(1"-" cos^2 170"°" ));