1. cosα=3/5. 0<α<π/2
sin²α+cos²α=1
sin²α+(3/5)²=1. sinα=+-√(1-9/25). по условию 0<α<π/2, ⇒sinα>0. sinα=4/5
tgα=sinα/cosα. tgα=(4/5):(3/5). tgα=4/3
ctgα=1/tgα. ctgα=3/4
2. sinα=1/2, π/2<α<α
cos²α=1-sin²α. cos²α=1-(1/2)². cos²α=3/4. cosα=+-√(3/4). π/2<α<π, ⇒ cosα<0. cosα=-√3/2
tgα=sinα/cosα. tgα=(1/2):(-√3/2). tgα=-√3
cgtα=-1/√3
3. cosα=-0,6. π<α<3π/2
sin²α=1-cos²α. sin²α=1-(-0,6)². sinα=+-√0,64. π<α<3π/2,⇒ sinα<0. sinα=-0,8
tgα=-0,8:(=0,6). tgα=4/3
ctgα=3/4
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