# SAT Math Multiple Choice Question 989: Answer and Explanation

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**Question: 989**

**9.**

In the right triangle above, cos *x* = 0.8. What is the value of cos *y*?

- A.
- B.
- C.
- D.

**Correct Answer:** B

**Explanation:**

**B**

**Difficulty:** Easy

**Category:** Additional Topics in Math / Trigonometry

**Strategic Advice:** Whenever trig values are given as decimal numbers, convert them to fractions so you can use the ratios given by SOH CAH TOA.

**Getting to the Answer:** The decimal 0.8 equals , which should make you think of a 3:4:5 triangle. Indeed, that's exactly what this triangle is. Draw a quick sketch and use SOH CAH TOA to place the side lengths in the correct places, ensuring that cos *x* = . That is, label the side adjacent to angle *x* as 4 and the hypotenuse 5. The remaining side must have length 3.

Again by SOH CAH TOA (and looking at angle *y* this time), cos *y* = , choice (B).