SAT Math : Geometry

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1 : How To Find Out If Lines Are Perpendicular

Line  is given by .

Which of the following is perpendicular to ?

Possible Answers:

Correct answer:

Explanation:

Putting the equation of the line into slope-intercept form, we get

The slope of line , therefore, is .

In order for a line to be perpendicular to the given line, it must have a slope that is the negative reciprocal of line g's slope. 

The slope of any given line perpendicular to line g must be  when written in slope-intercept form. In other words, the equation of the perpendicular line must be  where k is any constant. 

Written in standard form, the equation of this perpendicular line must be 

Therefore, the most appropriate answer is 

Example Question #2 : How To Find Out If Lines Are Perpendicular

Given: Lines A, B, and C on the coordinate plane, as follows:

The equation of Line A is .

The equation of Line B is .

The equation of Line is .

Which of the following is a true statement?

Possible Answers:

Line A and Line C are perpendicular to each other, but Line B is perpendicular to neither Line A nor Line C.

None of the statements in the other choices is true.

Line A and Line B are perpendicular to each other, but Line C is perpendicular to neither Line A nor Line B.

No two of Line A, Line B, and Line C are perpendicular to each other.

Line B and Line C are perpendicular to each other, but Line A is perpendicular to neither Line B nor Line C.

Correct answer:

No two of Line A, Line B, and Line C are perpendicular to each other.

Explanation:

Two lines are perpendicular if and only if the product of their slopes is . Therefore, we need to find the slopes of all three lines.Rewrite the equation for each line in its slope-intercept form , where  is the slope of the line.

Line A:

 is already in this form. The slope of Line A is the coefficient of , which is 3.

Line B:

Isolate  by working the same operations on both sides:

The slope of Line B is the coefficient of , which is 3.

Line C:

The slope of Line C is the coefficient of , which is 3.

All three lines have slope 3, so the product of the slopes of any two of the lines is . Therefore, no two of the lines are perpendicular.

Example Question #1 : How To Find Out If Lines Are Perpendicular

Given: Lines A, B, and C on the coordinate plane, as follows:

The equation of Line A is  .

The equation of Line B is .

The equation of Line C is .

Which of the following is a true statement?

Possible Answers:

Line A and Line C are perpendicular to each other, but Line B is perpendicular to neither Line A nor Line C.

Line A and Line B are perpendicular to each other, but Line C is perpendicular to neither Line A nor Line B.

Line B and Line C are perpendicular to each other, but Line A is perpendicular to neither Line B nor Line C.

None of the statements in the other choices is true.

No two of Line A, Line B, and Line C are perpendicular to each other.

Correct answer:

Line A and Line B are perpendicular to each other, but Line C is perpendicular to neither Line A nor Line B.

Explanation:

Two lines are perpendicular if and only if the product of their slopes is . Therefore, we need to find the slopes of all three lines.

Rewrite the equation for each line in its slope-intercept form , where  is the slope of the line.

Line A:

Isolate  by working the same operations on both sides:

The slope of Line A is the coefficient of , which is .

 

Take the same steps with the equations of the other two lines:

Line B:

The slope of Line B is 

 

Line C:

The slope of Line C is .

 

The product of the slopes of Lines A and B is , so these two lines are perpendicular.

The product of the slopes of Lines A and C is , so these two lines are not perpendicular.

The product of the slopes of Lines B and C is , so these two lines are not perpendicular.

Example Question #7 : How To Find Out If Lines Are Perpendicular

Given: Lines A, B, and C on the coordinate plane, as follows:

Line A has intercepts  and .

Line B has intercepts  and .

Line C has intercepts  and .

Which of the following statements is true?

Possible Answers:

No two of Line A, Line B, and Line C are perpendicular to each other.

Line A and Line B are perpendicular to each other, but Line C is perpendicular to neither Line A nor Line B.

Line B and Line C are perpendicular to each other, but Line A is perpendicular to neither Line B nor Line C.

Line A and Line C are perpendicular to each other, but Line B is perpendicular to neither Line A nor Line C.

None of the statements in the other choices is true.

Correct answer:

No two of Line A, Line B, and Line C are perpendicular to each other.

Explanation:

The slope of each line, given the coordinates of two points through which they pass, can be calculated by substituting the point coordinates into the slope formula

.

Line A:

Setting  and substituting:

 

Line B:

Setting  and substituting:

 

Line C:

Setting  and substituting:

The product of the slopes of Line A and Line B is , as is the product of the slopes of Line C and Line B; Since neither product is equal to , neither pair of lines is perpendicular. Also, the slopes of Line A and Line C are equal, so the lines are parallel, not perpendicular.

Example Question #1 : How To Find Out If Lines Are Perpendicular

Which of the following lines is perpendicular to y=3x-4

Possible Answers:

y=-3x-4

y=\frac{1}{3}x-4

y=\frac{1}{3}x+4

y=-\frac{1}{3}x-4

Correct answer:

y=-\frac{1}{3}x-4

Explanation:

The line which is perpendicular has a slope which is the negative inverse of the slope of the original line. 

Example Question #471 : Geometry

Trans

Lines P and Q are parallel. Find the value of .

Possible Answers:

Correct answer:

Explanation:

Since these are complementary angles, we can set up the following equation.

 

Now we will use the quadratic formula to solve for .

Note, however, that the measure of an angle cannot be negative, so  is not a viable answer. The correct answer, then, is 

 

Example Question #82 : Coordinate Geometry

In the xy -plane, line is given by the equation 2x - 3y = 5. If line passes through the point (a ,1), what is the value of a ?

Possible Answers:
3
5
4
-1
-2
Correct answer: 4
Explanation:

The equation of line l relates x -values and y -values that lie along the line. The question is asking for the x -value of a point on the line whose y -value is 1, so we are looking for the x -value on the line when the y-value is 1. In the equation of the line, plug 1 in for and solve for x:

2x - 3(1) = 5

2x - 3 = 5

2x = 8

x = 4. So the missing x-value on line l is 4.

Example Question #91 : Lines

The equation of a line is: 2x + 9y = 71

Which of these points is on that line?

Possible Answers:

(-2,7)

(4,7)

(4,-7)

(-4,7)

(2,7)

Correct answer:

(4,7)

Explanation:

Test the difference combinations out starting with the most repeated number.  In this case, y = 7 appears most often in the answers.  Plug in y=7 and solve for x.  If the answer does not appear on the list, solve for the next most common coordinate.

2(x) + 9(7) = 71

2x + 63 = 71

2x = 8

x = 4

Therefore the answer is (4, 7)

Example Question #24 : Psat Mathematics

Which of the following lines contains the point (8, 9)?

Possible Answers:

\dpi{100} \small 8x=9y

\dpi{100} \small 3x+6=2y

\dpi{100} \small 3x+6=y

\dpi{100} \small 8x+9=y

\dpi{100} \small 3x-6=2y

Correct answer:

\dpi{100} \small 3x-6=2y

Explanation:

In order to find out which of these lines is correct, we simply plug in the values \dpi{100} \small x=8 and \dpi{100} \small y=9 into each equation and see if it balances.

The only one for which this will work is \dpi{100} \small 3x-6=2y

Example Question #472 : Geometry

\dpi{100} \small 5x+25y = 125

Which point lies on this line?

Possible Answers:

\dpi{100} \small (5,5)

\dpi{100} \small (1,5)

\dpi{100} \small (5,1)

\dpi{100} \small (1,4)

\dpi{100} \small (5,4)

Correct answer:

\dpi{100} \small (5,4)

Explanation:

\dpi{100} \small 5x+25y = 125

Test the coordinates to find the ordered pair that makes the equation of the line true:

\dpi{100} \small (5,4)

\dpi{100} \small 5 (5) + 25 (4) = 25 + 100 = 125

\dpi{100} \small (1,5)

\dpi{100} \small 5(1)+25(5)= 5+125=130

\dpi{100} \small (5,1)

\dpi{100} \small 5(5)+25(1)= 25+25=50

\dpi{100} \small (5,5)

\dpi{100} \small 5(5)+25(5)= 25+125=150

\dpi{100} \small (1,4)

\dpi{100} \small 5(1)+25(4)= 5+100=105

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