SAT Math · Nonlinear equations in one variable · medium

What is the larger of the two solutions to |4x - 8| = 3x?

What is the larger of the two solutions to ∣4x−8∣=3x|4x - 8| = 3x?

Answer and explanation

Answer: C: 8

Split ∣4x−8∣=3x|4x - 8| = 3x into two cases. Case 1: 4x−8=3x4x - 8 = 3x gives x=8x = 8. Case 2: 4x−8=−3x4x - 8 = -3x gives 7x=87x = 8, so x=87x = \frac{8}{7}. Both solutions give a nonnegative right side 3x3x, so both are valid. Check x=8x = 8: ∣24∣=24|24| = 24. Check x=87x = \frac{8}{7}: ∣327−8∣=247=3⋅87\left|\frac{32}{7} - 8\right| = \frac{24}{7} = 3 \cdot \frac{8}{7}. The larger solution is 8, choice C. Choice A (87\frac{8}{7}) is the smaller solution. Choice B (4) and choice D (12) do not satisfy the equation: ∣16−8∣=8≠12|16 - 8| = 8 \neq 12 and ∣48−8∣=40≠36|48 - 8| = 40 \neq 36.

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