Question

Line A passes through the points (1, -1) and (-2, 8).

​Line B is perpendicular to line A.
​Select the slope of line B below:

A) −3
B) −13
C) 3
D) 13

Answer 1

D) 1/3

General Formulas and Concepts:

Pre-Algebra

Order of Operations: BPEMDAS

1. Brackets
2. Parenthesis
3. Exponents
4. Multiplication
5. Division
6. Addition
7. Subtraction

• Left to Right

Algebra I

• Coordinates (x, y)
• Slope Formula:
  `\displaystyle m = (y_2-y_1)/(x_2-x_1)`
• Perpendicular lines are the negative reciprocal to the given line

Explanation:

Step 1: Define

Identify

Point (1, -1)

Point (-2, 8)

Step 2: Find slope m

Simply plug in the 2 coordinates into the slope formula to find slope m.

Line A

1. Substitute in points [Slope Formula]:
   `\displaystyle m = (8--1)/(-2-1)`
2. [Fraction] Subtract:
   `\displaystyle m = (9)/(-3)`
3. [Fraction] Divide:
   `\displaystyle m = -3`

Line B

1. Negative:
   `\displaystyle m = 3`
2. Reciprocate:
   `\displaystyle m = (1)/(3)`