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4: Celsius degrees can be transformed in Fahrenheit degrees by using the formula : °C=(5/9)· (°F-32). What is x, if x degrees Celsius is equal to x degrees Fahrenheit?

　　(a) 40

　　(b) -40

　　(c) -20

　　(d) 20

　　(e) -30

Answer:

x = (5/9)· (x - 32).

9·x = 5·(x - 32).

In conclusion, x = -40C = -40F

5: In the (x,y) plane, what is the equation of the line that passes through the points (0,5) and (4,0)?

　　(a) y = (5/4) · x + 4

　　(b) y = (4/5) · x - 4

　　(c) y = (4/5) · x + 4

　　(d) y = -(5/4) · x + 5

　　(e) y = (5/4) · x + 5

Answer:

The equation of a line is y = m · x + n

First point, x = 0, y = 5, results in 5 = n

Second point: x = 4, y = 0, means 0 = m · 4 + n, or m = -n/4 or m= -5/4.

In conclusion, y = -(5/4) · x + 5 is the correct answer.

6: What is the value of (x + 2y) 2 if x 2 + 4 · y 2 = 2 and x · y = 3

　　(a) 13

　　(b) 14

　　(c) 16

　　(d) 18

　　(e) 22

Answer:

(x + 2y) 2 = x 2 + 4 · y 2 + 4 · x · y = 2 + 12 = 14

延伸阅读：

SAT数学专项练习题（三）

SAT数学专项练习题（四）

SAT数学专项练习题（五）

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