Modulus Inequalities (Leaving Cert Mathematics): Flashcards

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Modulus Inequalities
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General form of a modulus inequality

∣ax+b∣|ax+b| where aa, bb are constants

First step to solve ∣2x−3∣<5|2x-3|<5

Square both sides

(2x−3)2<25(2x-3)^2<25 simplifies to

4x2−12x−16<04x^2-12x-16<0

Factored form of 4x2−12x−16<04x^2-12x-16<0

(x−4)(x+1)<0(x-4)(x+1)<0

What is the region test method?

Pick values outside and between critical points to test inequality

Critical points in (x−4)(x+1)<0(x-4)(x+1)<0

−1-1 and 44

Does x=0x=0 satisfy ∣2x−3∣<5|2x-3|<5?

Yes, 3<53<5

Does x=5x=5 satisfy ∣2x−3∣<5|2x-3|<5?

No, 7≮57 \not< 5

Does x=−2x=-2 satisfy ∣2x−3∣<5|2x-3|<5?

No, 7≮57 \not< 5

Solution to ∣2x−3∣<5|2x-3|<5

−1<x<4-1<x<4

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