Question

given that sin theta= 1/4, 0 is less than theta but less than pi/2, what is the exact value of cos theta

Answer 1

Answer:

$\cos{\theta} = \frac{\sqrt{15}}{4}$

Step-by-step explanation:

For any angle $\theta$, we have that:

$(\sin{\theta})^{2} + (\cos{\theta})^{2} = 1$

Quadrant:

$0 \leq \theta \leq \frac{\pi}{2}$ means that $\theta$ is in the first quadrant. This means that both the sine and the cosine have positive values.

Find the cosine:

$(\sin{\theta})^{2} + (\cos{\theta})^{2} = 1$

$(\frac{1}{4})^{2} + (\cos{\theta})^{2} = 1$

$\frac{1}{16} + (\cos{\theta})^{2} = 1$

$(\cos{\theta})^{2} = 1 - \frac{1}{16}$

$(\cos{\theta})^{2} = \frac{16-1}{16}$

$(\cos{\theta})^{2} = \frac{15}{16}$

$\cos{\theta} = \pm \sqrt{\frac{15}{16}}$

Since the angle is in the first quadrant, the cosine is positive.

$\cos{\theta} = \frac{\sqrt{15}}{4}$