AlgebraHardTwo-step: find a, then the x-intercept
Algebra practice question
The graph of ax + 3y = 21 passes through the point (2, 5). What is the x-intercept of the graph?
- A. (7, 0)Correct
- B. (3, 0)
- C. (21, 0)
- D. (10.5, 0)
Answer: A. (7, 0)
From the point: 2a + 15 = 21, so a = 3. Setting y = 0 in 3x + 3y = 21 gives x = 7.
Why the other answers are wrong
- B. (3, 0)
- 3 is the value of a itself, not the x-intercept.
- C. (21, 0)
- 21 is the constant term; divide by a = 3 to get x = 7.
- D. (10.5, 0)
- 10.5 divides 21 by 2 — first find a = 3 from the given point.
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