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Given that sin theta= -16/65 and that angle theta terminates in quadrant 4, then what is the value of cosө


Sagot :

Answer:

[tex]\frac{63}{65}[/tex]

Step-by-step explanation:

The angle theta terminates in quadrant 4, so we know [tex]\frac{3\pi}{2} < \theta < 2\pi[/tex] and that the sin is negative and the cos is positive.

Using the Pythagorean identity [tex]\sin^2\theta+\cos^2\theta=1[/tex], we substitute [tex]\sin\theta[/tex] to find [tex]\cos\theta[/tex] :

[tex](-\frac{16}{65})^2+\cos^2\theta=1[/tex].

Solving for [tex]\cos\theta[/tex], we have

[tex]\cos^2\theta=1-\frac{256}{4225}\\[/tex],

[tex]\cos^2\theta=\frac{3969}{4225}[/tex].

Taking the square root of both sides gives

[tex]\cos\theta=\pm\frac{63}{65}[/tex].

We found before that since the angle theta terminates in quadrant 4, the cos is positive, so we take the positive square root to get

[tex]\cos\theta=\frac{63}{65}[/tex].