Find the solution to the system: y = 3x − 4 and y = −x + 2.
- (a)(1, −1)
- (b)(0, 2)
- (c)(1.5, 0.5)
- (d)(1.5, −3.5)
Answer
Why
Correct — C. Both equations give y, so set the right-hand sides equal.
3x − 4 = −x + 2
Add x to both sides: 4x − 4 = 2
Add 4: 4x = 6
Divide by 4: x = 1.5
Substitute into y = −x + 2: y = −1.5 + 2 = 0.5
Check in y = 3x − 4: 4.5 − 4 = 0.5 ✓
The lines meet at (1.5, 0.5) → option (c)
Why the others are wrong
- (a)(1, −1) — (1, −1) fits y = 3x − 4, since 3 − 4 = −1, but fails y = −x + 2: −1 + 2 = 1, not −1. It lies on the first line only.
- (b)(0, 2) — (0, 2) is where y = −x + 2 crosses the y-axis. In y = 3x − 4, x = 0 gives y = −4, not 2, so the point is not on the first line.
- (d)(1.5, −3.5) — (1.5, −3.5) has the right x but the wrong y: at x = 1.5 both lines give 0.5. Writing −1.5 − 2 instead of −1.5 + 2 is what produces −3.5.
Concept
A system's solution is the point that satisfies both equations at once: the point where the two lines cross.
The slopes here are 3 and −1. Different slopes mean the lines are not parallel, so they meet at exactly one point.
When both equations already read y = …, setting them equal removes y in one step.
Options (a) and (b) each pass one equation: (1, −1) lies on y = 3x − 4 and (0, 2) lies on y = −x + 2. A check in one equation alone lets one of them through, so test the point in both.
Key facts
- A solution of a system must satisfy every equation in it.
- Lines y = m₁x + c₁ and y = m₂x + c₂ with m₁ ≠ m₂ meet at exactly one point.
- Equal slopes with different intercepts give parallel lines and no solution.
Study next
Common traps
- Testing an option in one equation only: (1, −1) passes y = 3x − 4 and (0, 2) passes y = −x + 2.
- Stopping at x = 1.5: options (c) and (d) share that x, so the y has to be worked out and checked.
15 Sep 2025, 12:30, Quant Q.20 uses the same set-equal method on y = 2x + 1 and y = −x + 4, keyed (1, 3).
There every wrong option lies on y = 2x + 1, so the second equation is what separates them.
Related PYQs
No directly related past PYQ was found.