SAT Math Multiple Choice Question 778: Answer and Explanation

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Question: 778

13. Images

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.

Images

We can find the third side of the triangle with the Pythagorean Theorem (82 + x2 = 102), 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.

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