Question

Срочно эти два примера.

Answer 1

$3); ; sina= frac{5}{13}; ,; ; tga=?\\0^circ leq a textless 90^circ quad Rightarrow ; ; ; cosa textgreater 0; ,; ; tga textgreater 0\\cosa=+sqrt{1-sin^2a}=sqrt{1-frac{25}{169}}=sqrt{frac{144}{169}}= frac{12}{13} \\tga= frac{sina}{cosa}= frac{5/13}{12/13}= frac{5}{12} \\4); ; cosa=-frac{8}{17} textless 0; ; ; Rightarrow; ; ; 90^circ textless a textless 270^circ \\sina=pm sqrt{1-cos^2a}=pm sqrt{1-frac{64}{289}}=pm sqrt{ frac{225}{289} } =pm frac{15}{17}\\ctga= frac{cosa}{sina}=frac{-8/17}{pm15/17} =pm frac{8}{15}$

$ctga=-frac{8}{15}; ,; ; esli; ; 90^circ textless a textless 180^circ \\ctga=frac{8}{15}; ,; ; esli; ; 180^circ textless a textless 270^circ$