Дано cosα= -5/13, π<α<3π/2 Найти cosα/2, ctgα

Question

Дано cosα= -5/13, π<α<3π/2<br>
Найти cosα/2, ctgα

Answer 1

Cosa=-5/13
sina=-√(1-cos²a)=-√(1-25/169)=-√(144/169)=-12/13
ctga=cosa/sina=-5/13:(-12/13)=5/13*13/12=5/12
cos²a/2=(1+cosa)/2=(1-5/13)/2=8/13:2=4/13
cosa/2=+-2/√13

Answer 2

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