Coordinate Geometry and Graph Interpretation

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GRE Quantitative Reasoning › Coordinate Geometry and Graph Interpretation

Questions 1 - 10
1

A line has equation $2x+5y=10$. What is the slope of the line?

$\frac{2}{5}$

$-\frac{2}{5}$

$10$

$-\frac{5}{2}$

$\frac{5}{2}$

Explanation

This question tests graph interpretation, requiring the slope from a line equation in standard form. To find the slope, rewrite 2x + 5y = 10 as y = -2/5 x + 2, where -2/5 is the slope. This form highlights the negative slope and y-intercept of 2. Applying the conversion confirms the slope as -2/5. Thus, the correct answer is -2/5, choice A. A common incorrect option is -5/2, from swapping numerator and denominator. Another mistake could be forgetting the negative sign, leading to 2/5.

2

Line $p$ has equation $y=-\frac{1}{3}x+4$. What is the $y$-intercept of line $p$?

$\frac{1}{3}$

$4$

$-4$

$(4,0)$

$-\frac{1}{3}$

Explanation

This question tests coordinate geometry, specifically identifying the y-intercept from a line equation. In the equation y = -1/3x + 4, which is in slope-intercept form y = mx + b, the constant term b represents the y-intercept. The y-intercept is 4, which is the y-value when x = 0: y = -1/3(0) + 4 = 4. This means the line crosses the y-axis at the point (0,4). Students often confuse the slope (-1/3) with the y-intercept or mistakenly write the y-intercept as a coordinate pair like (4,0).

3

A line has equation $y= -\frac{3}{2}x+6$. If the line is shifted right by 2 units (with no vertical shift), which of the following is an equation of the new line?

$y=-\frac{3}{2}(x+2)+6$

$y=-\frac{3}{2}(x-2)+6$

$y=-\frac{3}{2}x+3$

$y=\frac{3}{2}x+6$

$y=-\frac{3}{2}x+9$

Explanation

This question tests graph interpretation, applying a horizontal shift to the line y = -3/2 x + 6. Shifting right by 2 replaces x with (x-2), yielding y = -3/2 (x-2) + 6. This maintains the slope but adjusts the intercept. Expanding gives y = -3/2 x + 9, equivalent to the form in C. Therefore, Choice C is correct. A common mistake is shifting left, leading to (x+2). Another error could be vertical shift confusion, altering the constant incorrectly.

4

The line with equation $3x+2y=12$ is graphed in the $xy$-plane. What is the $y$-intercept of the line?​

$4$

$-6$

$-4$

$6$

$\frac{3}{2}$

Explanation

This question tests graph interpretation, specifically finding the y-intercept from a linear equation in standard form. The y-intercept occurs where the line crosses the y-axis, which is when x = 0. Substituting x = 0 into 3x + 2y = 12 gives: 3(0) + 2y = 12, so 2y = 12, and y = 6. Therefore, the y-intercept is 6, or the point (0,6). A common mistake is confusing the y-intercept with the x-intercept (which would be 4) or misidentifying coefficients as intercepts.

5

Two lines are given by $y=\frac{3}{4}x+1$ and $y=\frac{3}{4}x-5$. Which of the following best describes the relationship between the two lines?

They intersect at exactly one point.

They are the same line.

They intersect on the $y$-axis.

They are parallel and distinct.

They are perpendicular.

Explanation

This question tests graph interpretation, comparing slopes and intercepts to determine line relationships. Both lines have slope 3/4 but different y-intercepts (1 and -5), indicating they are parallel and distinct. Parallel lines never intersect and maintain constant distance. This relationship is confirmed by the identical slopes and unequal intercepts. Thus, Choice C is correct. A common mistake is assuming they intersect at one point due to similar slopes. Another error could be thinking they are the same line if intercepts are miscompared.

6

The line $y=x-4$ is shifted upward by $6$ units to form a new line. What is the $y$-intercept of the new line?

$-6$

$10$

$4$

$2$

$-10$

Explanation

This question tests graph interpretation, specifically understanding vertical translations of linear functions. The original line y = x - 4 has y-intercept -4 (when x = 0, y = -4). When a line is shifted upward by 6 units, we add 6 to the entire equation: y = x - 4 + 6 = x + 2. The new line has equation y = x + 2, so its y-intercept is 2. This vertical shift moves every point on the line up by 6 units, including the y-intercept which moves from -4 to 2. A common error is subtracting instead of adding the shift amount.

7

A line has equation $y=3x-7$. What is the $y$-intercept of the line?

$(0,7)$

$3$

$-\frac{7}{3}$

$-7$

$7$

Explanation

This question tests graph interpretation, specifically identifying the y-intercept from a line equation in slope-intercept form. The equation y = 3x - 7 is already in the form y = mx + b, where b is the y-intercept. The y-intercept occurs when x = 0, giving y = 3(0) - 7 = -7. Therefore, the y-intercept is -7, which represents the point where the line crosses the y-axis. A common mistake is confusing the slope (3) with the y-intercept or misidentifying the sign, thinking the y-intercept is positive 7.

8

On the coordinate plane, a line is described as crossing the $y$-axis at $(0,-2)$ and the $x$-axis at $(5,0)$. What is the slope of the line?

$-\frac{5}{2}$

$-\frac{2}{5}$

$\frac{5}{2}$

$\frac{2}{5}$

$-2$

Explanation

This question tests graph interpretation, calculating slope from x- and y-intercepts. The points (0,-2) and (5,0) give slope m = (0 - (-2))/(5 - 0) = 2/5. This positive slope shows the line rising from left to right. Applying the formula confirms this value. Therefore, Choice A is correct. A common incorrect option is -2/5, from neglecting the double negative. Another mistake might be inverting to 5/2.

9

Line $m$ has equation $y=-4x+9$. What is the slope of line $m$?

$-\frac{9}{4}$

$-4$

$9$

$\frac{9}{4}$

$4$

Explanation

This question tests graph interpretation, specifically identifying the slope from a line equation in slope-intercept form. The equation y = -4x + 9 follows the pattern y = mx + b, where m is the slope and b is the y-intercept. The coefficient of x is -4, so the slope is -4. This means the line decreases by 4 units vertically for every 1 unit increase horizontally. A common error is confusing the slope with the y-intercept (9) or misreading the negative sign, leading to answers like 4 or 9/4.

10

Line $m$ has equation $y=3x-7$. What is the $y$-intercept of line $m$?

$-7$

$3$

$-\frac{7}{3}$

$7$

$-3$

Explanation

This question tests graph interpretation, focusing on identifying the y-intercept from a line's equation in slope-intercept form. The y-intercept is the value of y where the line crosses the y-axis, represented by the constant term b in y = mx + b. For the equation y = 3x - 7, the slope m is 3, and the y-intercept b is -7. This directly gives the y-intercept as -7. Therefore, the correct answer is -7, which is choice B. A common mistake is confusing the y-intercept with the slope, leading to selecting 3. Another error might involve misreading the sign, resulting in choices like 7.

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