AlgebraMediumSlope of a line reflected across the y-axis
Algebra practice question
In the xy-plane, line ℓ has equation y = 5x − 3. Line m is the reflection of line ℓ across the y-axis. What is the slope of line m?
Answer: -5
Reflecting across the y-axis replaces x with −x: y = 5(−x) − 3 = −5x − 3. The slope is −5.
Common wrong answers
- If you answered 3
- 3 is the y-intercept's magnitude, not the slope.
- If you answered 5
- 5 is the slope of ℓ itself; reflecting across the y-axis reverses the sign of the slope.
- If you answered -1/5
- −1/5 is the slope of a perpendicular line, not a reflection.
More Algebra questions
- Medium
A system: 2x + y = 11 and x − y = 1. What is the value of x + y? - Medium
Which of the following describes all solutions to 4x − 9 ≤ 2x + 5? - Medium
A phone's battery percentage is modeled by P = 100 − 8t, where t is the number of hours since it was unplugged… - Medium
If y = 2x − 1 and 3x + y = 14, what is the value of x? - Medium
If |2x − 3| = 7, what is the sum of all possible values of x? - Medium
Line k has equation y = (2/3)x + 1. Which equation represents a line perpendicular to line k?
Not affiliated with the College Board. SAT is a trademark of the College Board.