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【官方】SAT数学每日一题附答案和解析(2018年1月12日)

小站整理2018-01-31 11:20:52

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摘要：每日一题的内容是由sat官方所出，质量虽不比真题，但备考期间，由于有效备考资料珍贵有限。大家可以每天拿官方的Daily Practice来练手。以下是2018年1月10日的SAT数学练习部分：

每日一练

Mathematics>Standard Multiple Choice

Read the following SAT test question and thenclick on a button to select your answer.

y=x+a

y=-x+a

In the system of equations above, a is a positive constant. If the system is graphed in the xy-plane, which of the following best describes the two lines?

A.Both equations represent the same line.

B.The lines are parallel.

C.The lines are perpendicular.

D.The lines intersect but are not perpendicular.

答案：C

解析：

Let's examine the slope and y-intercept of both graphs.

Both equations are written in slope-intercept form: y=mx+b

where m is the graph's slope and b is the graph's y-intercept.

The graph of the first equation, y=x+a, has a slope of 1 and its y-intercept is a.

The graph of the second equation, y=-x+a, has a slope of -1. Its y-intercept is also a. Therefore, the y-intercepts are the same; the slope of the first equation's graph is the negative of the reciprocal of the slope of the second equation's graph (the reciprocal of 1/1 is 1/1), which means that the lines are perpendicular.

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