答:(1)三角的定义： 角α顶点放在坐标原点o，始边放在x轴上，在终边上任取一点p(x,y),op=r那么：sinα=y/r cosα=x/r tanα=y/x cotα=x/y (2)诱导公式有：Sin(2kπ+α)=sinα cos(2kπ+α)=cosα tan(2kπ+α)=tanα Sin(π-α)=sinα cos(π-α)=-cosα tan(π-α)=-tanα sin(π+α) =-sinα cos(π+α)=-cosα tan(π+α)=tanα sin(2π-α)=-sinα cos(2π-α)=cosα tan(2π-α)=-tanα sin(-α)=-sinα cos(-α)=cosα tan(-α)=tanα sin(π/2-α)=cosα cos(π/2-α)=sinα sin(π/2+α)=cosα cos(π/2+α)=-sinα sin(3π/2-α)=-cosα cos(3π/2-α)=-sinα sin(3π/2+α)=-cosα cos(3π/2+α)=sinα (3)(sin^2)α+(cos^2)α=1 tanα=sinα/cosα tanα·cotα=1 注“^2”表示平方。 (4)sin(α±β) =sinαcosβ±cosαsinβ cos(α-β) = cosαcosβ+sinαsinβ cos(α+β) = cosαcosβ-sinαsinβ tan(α+β) =(tanα+tanβ)/(1-tanα·tanβ) tan(α-β) =(tanα- tanβ)/(1+tanα·tanβ) (5)sin2α=2sinαcosα tan2α=2tanα/[1-(tan^2)α] cos2α=(cos^2)α-(sin^2)α =1- 2(sin^2)α =2(cos^2)α-1