AlgebraVery hardUnknown coordinate from two perpendicular segments
Algebra practice question
In the xy-plane, the line through (1, 2) and (4, k) is perpendicular to the line through (0, 0) and (3, −1). What is the value of k?
Answer: 11
The second line has slope −1/3, so the first has slope 3: (k − 2)/(4 − 1) = 3 gives k = 11.
Common wrong answers
- If you answered 1
- 1 uses slope −1/3 (parallel, not perpendicular).
- If you answered 3
- 3 uses slope 1/3.
- If you answered -7
- −7 uses slope −3.
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