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The area of the region satisfying the inequalities ∣x∣−y≤1,y≥0|\mathrm{x}|-\mathrm{y} \leq 1, \mathrm{y} \geq 0 and y≤1\mathrm{y} \leq 1 is

Entered answer:

Solution

✅ Correct Answer: 3

We need to find the area of the region where all three conditions are satisfied:

∣x∣−y≤1|x| - y \leq 1, y≥0y \geq 0, and y≤1y \leq 1


Rewrite the first inequality as y≥∣x∣−1y \geq |x| - 1.

Since ∣x∣=x|x| = x when x≥0x \geq 0 and ∣x∣=−x|x| = -x when x<0x < 0:

  • When x≥0x \geq 0: y≥x−1y \geq x - 1
  • When x<0x < 0: y≥−x−1y \geq -x - 1

Find the key intersection points by solving where boundary lines meet:

Where y=x−1y = x - 1 meets y=0y = 0: 0=x−10 = x - 1, so x=1x = 1

Point: (1,0)(1, 0)

Where y=−x−1y = -x - 1 meets y=0y = 0: 0=−x−10 = -x - 1, so x=−1x = -1

Point: (−1,0)(-1, 0)

Where y=x−1y = x - 1 meets y=1y = 1: 1=x−11 = x - 1, so x=2x = 2

Point: (2,1)(2, 1)

Where y=−x−1y = -x - 1 meets y=1y = 1: 1=−x−11 = -x - 1, so x=−2x = -2

Point: (−2,1)(-2, 1)


From y≥∣x∣−1y \geq |x| - 1, we get ∣x∣≤y+1|x| \leq y + 1

This means −(y+1)≤x≤(y+1)-(y + 1) \leq x \leq (y + 1)

For any yy between 00 and 11, the width of the region is 2(y+1)2(y + 1)


The region forms a trapezoid:

At y=0y = 0: width =2(0+1)=2= 2(0 + 1) = 2 (from x=−1x = -1 to x=1x = 1)

At y=1y = 1: width =2(1+1)=4= 2(1 + 1) = 4 (from x=−2x = -2 to x=2x = 2)

Height =1−0=1= 1 - 0 = 1

Area of trapezoid:

Area=12×(sum of parallel sides)×height\text{Area} = \dfrac{1}{2} \times (\text{sum of parallel sides}) \times \text{height}

Area=12×(2+4)×1=12×6×1=3\text{Area} = \dfrac{1}{2} \times (2 + 4) \times 1 = \dfrac{1}{2} \times 6 \times 1 = 3

The area of the region is 33 square units.

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