Porisma

Worked solution

Compare a V graph with a logarithm across a pole

Solve graphically the inequality ∣x+2∣≥ln⁡(x2−2x+1)|x+2|\geq\ln(x^2-2x+1). marks

[2016/SRJC/Promo/1]

CJC · Review Problems · Question 12

Answer

(−∞,α]∪[β,1)∪(1,∞)(-\infty,\alpha]\cup[\beta,1)\cup(1,\infty), where α≈−5.85\alpha\approx-5.85, β≈−0.812\beta\approx-0.812 are the intersections.

Graphical solution

The logarithm requires (x−1)2>0(x-1)^2>0, so x≠1x\ne1. It has vertical asymptote x=1x=1. Sketch y=∣x+2∣y=|x+2| and y=ln⁡((x−1)2)y=\ln((x-1)^2) on the same axes. The source gives intersections approximately (−5.85,3.85)(-5.85,3.85) and (−0.812,1.19)(-0.812,1.19). Read where the V graph is on or above the logarithm: in the printed three-significant-figure form, x≤−5.85x\leq-5.85 or −0.812≤x<1-0.812\leq x<1 or x>1x>1.

How did this part go?

Boundary precision

Let α<β<1\alpha<\beta<1 be the two exact intersection inputs satisfying ∣x+2∣=ln⁡((x−1)2)|x+2|=\ln((x-1)^2). Numerically α≈−5.847877501\alpha\approx-5.847877501 and β≈−0.811590083\beta\approx-0.811590083. The exact set is (−∞,α]∪[β,1)∪(1,∞)(-\infty,\alpha]\cup[\beta,1)\cup(1,\infty). The displayed source decimals are rounded graph readings, not exact thresholds.

How did this part go?

Compare your sketch

Expand diagram

Use the scrollbars or arrow keys to inspect details.

The V graph y=|x+2| has vertex (−2,0). The logarithm y=ln((x−1)²) has vertical asymptote x=1 and axis crossings 0 and 2. Intersections are approximately (−5.85,3.85) and (−0.812,1.19). The V lies on or above the log for x≤alpha, beta≤x<1 and x>1.
The V graph y=|x+2| has vertex (−2,0). The logarithm y=ln((x−1)²) has vertical asymptote x=1 and axis crossings 0 and 2. Intersections are approximately (−5.85,3.85) and (−0.812,1.19). The V lies on or above the log for x≤alpha, beta≤x<1 and x>1.
The V graph y=|x+2| has vertex (−2,0). The logarithm y=ln((x−1)²) has vertical asymptote x=1 and axis crossings 0 and 2. Intersections are approximately (−5.85,3.85) and (−0.812,1.19). The V lies on or above the log for x≤alpha, beta≤x<1 and x>1.

Common mistakes

Equality includes the two curve intersections, but x=1 stays excluded because the logarithm is undefined.

Solution notes

The diagrams are independently reconstructed mathematical equivalents. The plotted geometry is illustrative; use the labelled exact or approximate values and the stated domain.

Read the hint