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각 $\theta_1$theta, start subscript, 1, end subscript은 사분면 $\text{IV}$start text, I, V, end text에 있고, $\sin(\theta_1)=-\dfrac{13}{85}$sine, left parenthesis, theta, start subscript, 1, end subscript, right parenthesis, equals, minus, start fraction, 13, divided by, 85, end fraction 입니다.

$\cos(\theta_1)=$cosine, left parenthesis, theta, start subscript, 1, end subscript, right parenthesis, equals