SAT Math · Systems of equations in two variables · medium

The graphs of y = x² - 3 and y = 4x - 3 intersect at two points. What is the product of the x-coordinates of these two points?

The graphs of y=x2−3y = x^2 - 3 and y=4x−3y = 4x - 3 intersect at two points. What is the product of the xx-coordinates of these two points?

Answer and explanation

Answer: C: 0

Set the two expressions for yy equal: x2−3=4x−3x^2 - 3 = 4x - 3. Add 3 to both sides and subtract 4x4x: x2−4x=0x^2 - 4x = 0, which factors as x(x−4)=0x(x - 4) = 0. The intersections are at x=0x = 0 and x=4x = 4, and the product of the xx-coordinates is 0×4=00 \times 4 = 0, choice C. Vieta's formulas agree: the product of the roots is the constant term, which is 0. Choice A (4) is the sum of the roots, or the nonzero root. Choice B (−3-3) is the constant from the original equations, which cancels. Choice D (3) is the same constant with a sign slip.

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