Mathematics

Mathematics

Problem

For which value of kk will the inequality kx>8kx>8 have exactly the same solution set as x<−4x<-4? a) k=−4k=-4 b) k=−2k=-2 c) k=2k=2 d) k=−8k=-8
Intuitive explanation

The key is recognizing that when you divide or multiply an inequality by a negative number, the inequality sign flips. Since x<−4x < -4 is already solved for xx, you need to manipulate kx>8kx > 8 to match it exactly—which means kk must be negative. Work backwards: if kx>8kx > 8 should give x<−4x < -4, divide both sides by kk and use the sign-flip rule to find what kk must be.

Intuitive explanation

The key is recognizing that when you divide or multiply an inequality by a negative number, the inequality sign flips. Since x<−4x < -4 is already solved for xx, you need to manipulate kx>8kx > 8 to match it exactly—which means kk must be negative. Work backwards: if kx>8kx > 8 should give x<−4x < -4, divide both sides by kk and use the sign-flip rule to find what kk must be.

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