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Algebra / Linear equations in two variables Difficulty: Hard

Line p is defined by 4y+8x=6. Line r is perpendicular to line p in the xy-plane. What is the slope of line r ?

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Explanation

The correct answer is 12. For an equation in slope-intercept form y=mx+b, m represents the slope of the line in the xy-plane defined by this equation. It's given that line p is defined by 4y+8x=6. Subtracting 8x from both sides of this equation yields 4y=-8x+6. Dividing both sides of this equation by 4 yields y=-84x+64, or y=-2x+32. Thus, the slope of line p is -2 . If line r is perpendicular to line p , then the slope of line r is the negative reciprocal of the slope of line p . The negative reciprocal of -2 is -1-2=12. Note that 1/2 and .5 are examples of ways to enter a correct answer.