PSAT Math : Geometry

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #3 : How To Find X Or Y Intercept

A line has the equation: x+y=1.

What is the y-intercept?

Possible Answers:

1

2

0.5

0

-1

Correct answer:

1

Explanation:

x+y=1 can be rearranged into: y=-x+1. Using the point-slope form, we can see that the y-intercept is 1.

Example Question #4 : How To Find X Or Y Intercept

A line has the equation: 2x+4y=8. 

What is the x-intercept?

Possible Answers:

-4

-8

0

4

8

Correct answer:

4

Explanation:

To find the x-intercept, rearrange the equation 2x+4y=8 so that x is isolated:

2x=-4y+8

x=-2y+4

Using the point-slope formula, we see that the x-intercept is 4.

Example Question #222 : Coordinate Geometry

Given the line \(\displaystyle 4x + 3y = 12\), what is the sum of the \(\displaystyle x\)-intercept and the \(\displaystyle y\)-intercept?

Possible Answers:

\(\displaystyle 7\)

\(\displaystyle 1\)

\(\displaystyle 3\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle 7\)

Explanation:

Intercepts occur when a line crosses the \(\displaystyle x\)-axis or the \(\displaystyle y\)-axis. When the line crosses the \(\displaystyle x\)-axis, then \(\displaystyle y = 0\) and \(\displaystyle x = 3\).  When the line crosses the \(\displaystyle y\)-axis, then \(\displaystyle x = 0\) and \(\displaystyle y = 4\). The intercept points are \(\displaystyle (0, 4)\) and \(\displaystyle (3, 0 )\). So the \(\displaystyle y\)-intercept is \(\displaystyle 4\) and the \(\displaystyle x\) intercept is \(\displaystyle 3\) and the sum is \(\displaystyle 7\).

Example Question #591 : Geometry

What is the y intercept of the following function of x? 

y = 3x 

Possible Answers:

–1

1

–3

3

0

Correct answer:

0

Explanation:

The answer is 0 because in slope intercept form, y = mx + b; b is the y intercept. In this case b = 0. 

Example Question #2 : How To Find X Or Y Intercept

What is the x-intercept of a line with a slope of 5 and y-intercept of 3.5?

Possible Answers:

(–3.5, 0)

(0.7, 0)

(3.5, 0)

(0, –0.7)

(–0.7, 0)

Correct answer:

(–0.7, 0)

Explanation:

To solve this, first find the equation of our line.  The form of the question gives it to us very directly.  We can use the slope-intercept form (y = mx + b).

y = 5x + 3.5

The x-intercept is found by setting y = 0, because that will give us the x-value at which the line crosses the x-axis.

0 = 5x + 3.5; –3.5 = 5x; x = –3.5 / 5 or –0.7.  The point will be (–0.7, 0)

Example Question #1 : How To Find X Or Y Intercept

Determine the y-intercept of the following line:

\dpi{100} \small 3x+6y=9\(\displaystyle \dpi{100} \small 3x+6y=9\)

Possible Answers:

\dpi{100} \small 6\(\displaystyle \dpi{100} \small 6\)

\dpi{100} \small 1.5\(\displaystyle \dpi{100} \small 1.5\)

\dpi{100} \small \frac{1}{3}\(\displaystyle \dpi{100} \small \frac{1}{3}\)

\dpi{100} \small 3\(\displaystyle \dpi{100} \small 3\)

\dpi{100} \small 9\(\displaystyle \dpi{100} \small 9\)

Correct answer:

\dpi{100} \small 1.5\(\displaystyle \dpi{100} \small 1.5\)

Explanation:

The y-intercept occurs when \dpi{100} \small x=0\(\displaystyle \dpi{100} \small x=0\)

\dpi{100} \small 3x+6y=9\(\displaystyle \dpi{100} \small 3x+6y=9\)

\dpi{100} \small 3(0)+6y=9\(\displaystyle \dpi{100} \small 3(0)+6y=9\)

\dpi{100} \small 0+6y=9\(\displaystyle \dpi{100} \small 0+6y=9\)

\dpi{100} \small y = \frac{9}{6}=1.5\(\displaystyle \dpi{100} \small y = \frac{9}{6}=1.5\)

Example Question #2 : How To Find X Or Y Intercept

At what point does the graph 3y-2x=31\(\displaystyle 3y-2x=31\) cross the \(\displaystyle y\)-axis?

Possible Answers:

\(\displaystyle \left ( 0,-\frac{2}{3} \right )\)

\(\displaystyle \left ( 0,\frac{31}{3} \right )\)

\(\displaystyle \left ( 0,\frac{3}{2} \right )\)

\(\displaystyle \left ( 0,\frac{2}{3} \right )\)

\(\displaystyle \left ( 0,\frac{3}{31} \right )\)

Correct answer:

\(\displaystyle \left ( 0,\frac{31}{3} \right )\)

Explanation:

The graph crosses the \(\displaystyle y\)-axis where x=0\(\displaystyle x=0\). So plugging in and solving yields \frac{31}{3}\(\displaystyle \frac{31}{3}\)

Example Question #11 : How To Find X Or Y Intercept

Find the x-intercepts of  25x^{2}+4y^{2} = 9\(\displaystyle 25x^{2}+4y^{2} = 9\).

Possible Answers:

\pm 5\(\displaystyle \pm 5\)

2\(\displaystyle 2\)

5\(\displaystyle 5\)

\pm \frac{3}{5}\(\displaystyle \pm \frac{3}{5}\)

\frac{3}{5}\(\displaystyle \frac{3}{5}\)

Correct answer:

\pm \frac{3}{5}\(\displaystyle \pm \frac{3}{5}\)

Explanation:

To find the x-intercepts, plug y=0\(\displaystyle y=0\) into the equation and solve for x\(\displaystyle x\).

25x^{2} + 4\cdot 0^{2} = 9\(\displaystyle 25x^{2} + 4\cdot 0^{2} = 9\)

25x^{2} = 9\(\displaystyle 25x^{2} = 9\)

x^{2} = \frac{9}{25}\(\displaystyle x^{2} = \frac{9}{25}\)

x = \pm \frac{3}{5}\(\displaystyle x = \pm \frac{3}{5}\)

Don't forget that there are two solutions, both negative and positive!

Example Question #11 : How To Find X Or Y Intercept

A line with the exquation y=x^2+3x+c\(\displaystyle y=x^2+3x+c\) passes through the point \(\displaystyle (-4,6)\).  What is the \(\displaystyle y\)-intercept?

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 4\)

\(\displaystyle 2\)

\(\displaystyle -2\)

\(\displaystyle -1\)

Correct answer:

\(\displaystyle 2\)

Explanation:

By plugging in the coordinate, we can figure out that \(\displaystyle c=2\).  The \(\displaystyle y\)-Intercept is when \(\displaystyle x=0\), plugging in 0 for \(\displaystyle x\) gives us \(\displaystyle y=2\).

Example Question #11 : X And Y Intercept

What are the \(\displaystyle x\)-intercept(s) of the following line:

\(\displaystyle y=x^2+12x+27\)

Possible Answers:

\(\displaystyle x=3,9\)

\(\displaystyle x=-3,-9\)

\(\displaystyle x=3,-9\)

\(\displaystyle x=-3,9\)

\(\displaystyle x=27,1\)

Correct answer:

\(\displaystyle x=-3,-9\)

Explanation:

We can factor \(\displaystyle y=x^2+12x+27\) and set \(\displaystyle y\) equal to zero to determine the \(\displaystyle x\)-intercepts.

\(\displaystyle y=(x+3)(x+9)\) satisfies this equation.

 

Therefore our \(\displaystyle x\)-intercepts are \(\displaystyle -3\) and \(\displaystyle -9\).

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