Question

Здравствуйте, помогите, пожалуйста ​

Answer 1

t - угол второй четверти значит Cost < 0 .

$1+tg^{2}t=\frac{1}{Cos^{2} t}\\\\Cos^{2}t=\frac{1}{1+tg^{2}t } =\frac{1}{1+(-\frac{20}{21})^{2} }=\frac{1}{1+\frac{400}{441} }=\frac{1}{\frac{841}{441} }=\frac{441}{841}\\\\Cost=-\sqrt{\frac{441}{841} }=-\frac{21}{29}\\\\tgt=\frac{Sint}{Cost} \\\\Sint=tgt*Cost=-\frac{20}{21} *(-\frac{21}{29})=\frac{20}{29}\\\\Ctgt=\frac{1}{tgt}=1:(-\frac{20}{21} )=-\frac{21}{20} \\\\\boxed{Sint=\frac{20}{29}} \\\\\boxed{Cost=-\frac{21}{29}}\\\\\boxed{Ctgt=-\frac{21}{20}}$