SAT Math · Linear equations in one variable · medium

For what values of k and c does the equation 5(x-2)+12 = kx+c have infinitely many solutions?

For what values of kk and cc does the equation 5(x−2)+12=kx+c5(x-2)+12 = kx+c have infinitely many solutions?

Answer and explanation

Answer: A: k=5 and c=2

Simplify the left side: 5(x−2)+12=5x−10+12=5x+25(x - 2) + 12 = 5x - 10 + 12 = 5x + 2. The equation is 5x+2=kx+c5x + 2 = kx + c. It has infinitely many solutions only when both sides are identical expressions, so k=5k = 5 and c=2c = 2, choice A. Choice B (k=5k = 5, c=6c = 6) matches the coefficient but not the constant, giving 2=62 = 6, so no solution. Choice C (k=6k = 6, c=2c = 2) gives exactly one solution, x=0x = 0. Choice D (k=5k = 5, c=−2c = -2) has a sign error and gives 2=−22 = -2, no solution. Both the coefficient and constant must match.

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