Question

If sin 0=8/17, and tan0<0, what is cos(0)

Use exact values. No decimals.
(0 means theta)

Answer 1

Answer: -15/17

Step-by-step explanation:

In the first quadrant, all sine, cosine and tan are all positive. In the second quadrant, only sine is positive. Third quadrant, only tangent is positive and fourth quadrant, only cosine is positive.

Therefore, when sine is positive and tan is negative, the angle can only be in quadrant 2. Then draw the triangle. Draw a triangle with the angle from the origin, with the opposite leg from the angle with value of 8 and the hypotenuse of value 17. Since cosine is what the question is asking for, and we know the data given forms an right triangle, the value of the other leg is 15. It is an 8-15-17 special triangle or use the Pythagorean Theorem.

Finally, taking the cosine of the angle from the origin gives -15/17 since it is in quadrant 2.

Answer 2

Answer: -15/17

Explanation:

sin ∅ = 8/17

If you drew a a line in the 2rd quadrant because tan ∅ <0, which means tan∅ is negative.

Tan∅= sin∅/cos∅

they told you sin∅ is positive which is related to your y.

but cos∅ needs to be negative which is related to x

This happens in the second quadrant x is negative and y is positive.

Now we know which way to draw our line. Label the opposite of the angle 8 and the hypotenuse 17 because sin∅ = 8/17

Use pythagorean to find adjacent.

17² = 8² + a²

225 = a²

a = 15

The adjacent is negative because the adjacent is on the x-axis in the negative direction.

cos ∅ = adj/hyp

cos∅ = -15/17