# SAT Math Multiple Choice Question 778: Answer and Explanation

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**Question: 778**

**13.**

In the figure above, if cos *A* = 0.8, what is the slope of line *l*?

- A. 0.60
- B. 0.75
- C. 0.90
- D. 1.10

**Correct Answer:** B

**Explanation:**

**B**

**Additional Topics (trigonometry/coordinate geometry) HARD**

If this question gave you trouble, review Chapter 10, particularly Lessons 3, 4, and 9. Since the question asks about the slope, we should draw in a right triangle to show the "rise" and "run" of the line. If cos *A* = 0.8, then the adjacent side of this triangle could be 8 and the hypotenuse could be 10 (because o/h = 8/10 = 0.8) as shown below.

We can find the third side of the triangle with the Pythagorean Theorem (8^{2} + *x*^{2} = 10^{2}), although it's easier to simply notice that this is a triangle in the 3-4-5 family: 6-8-10. Since the slope of a line is the rise over the run, the slope is 6/8 = 0.75.