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Area Under the Curves question

2023 · 6 Apr · Shift 2 · Q25
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  5. /2023 · 6 Apr · Shift 2 · Q25

Area Under the Curves question

2023 · 6 Apr · Shift 2 · Q25

JEE MainMathematicsArea Under the CurvesMCQ+4 / −1
The area bounded by the curves y=∣x−1∣+∣x−2∣y=|x-1|+|x-2|y=∣x−1∣+∣x−2∣ and y=3y=3y=3 is equal to :
  1. A
    5
  2. B
    4
  3. C
    6
  4. D
    3
View written solutionFree

Correct answer: B

  1. Break the absolute value function into intervals

We have y=∣x−1∣+∣x−2∣.y=|x-1|+|x-2|.y=∣x−1∣+∣x−2∣. The critical points are x=1x=1x=1 and x=2x=2x=2.

So we consider three regions:

  • For x<1x<1x<1: ∣x−1∣=1−x,∣x−2∣=2−x|x-1|=1-x,\quad |x-2|=2-x∣x−1∣=1−x,∣x−2∣=2−x Hence y=(1−x)+(2−x)=3−2x.y=(1-x)+(2-x)=3-2x.y=(1−x)+(2−x)=3−2x.

  • For 1≤x≤21\le x\le 21≤x≤2: ∣x−1∣=x−1,∣x−2∣=2−x|x-1|=x-1,\quad |x-2|=2-x∣x−1∣=x−1,∣x−2∣=2−x Hence y=(x−1)+(2−x)=1.y=(x-1)+(2-x)=1.y=(x−1)+(2−x)=1.

  • For x>2x>2x>2: ∣x−1∣=x−1,∣x−2∣=x−2|x-1|=x-1,\quad |x-2|=x-2∣x−1∣=x−1,∣x−2∣=x−2 Hence y=(x−1)+(x−2)=2x−3.y=(x-1)+(x-2)=2x-3.y=(x−1)+(x−2)=2x−3.

So the curve is:

3-2x, & x<1,\\ 1, & 1\le x\le 2,\\ 2x-3, & x>2. \end{cases}$$ 2. **Find points of intersection with $y=3$** We solve $$|x-1|+|x-2|=3.$$ Using the piecewise form: - For $x<1$: $$3-2x=3 \implies x=0.$$ - For $1\le x\le 2$: $$1=3$$ no solution. - For $x>2$: $$2x-3=3 \implies 2x=6 \implies x=3.$$ Thus the two curves meet at $x=0$ and $x=3$. 3. **Set up the bounded area** Between $x=0$ and $x=3$, the line $y=3$ lies above the curve $y=|x-1|+|x-2|$. Therefore, $$\text{Area}=\int_0^3 \left[3-\bigl(|x-1|+|x-2|\bigr)\right]dx.$$ Now evaluate piecewise. 4. **Compute the area on each interval** ### From $x=0$ to $x=1$ Here $y=3-2x$, so $$3-(3-2x)=2x.$$ Thus, $$A_1=\int_0^1 2x\,dx=\left[x^2\right]_0^1=1.$$ ### From $x=1$ to $x=2$ Here $y=1$, so $$3-1=2.$$ Thus, $$A_2=\int_1^2 2\,dx=2(2-1)=2.$$ ### From $x=2$ to $x=3$ Here $y=2x-3$, so $$3-(2x-3)=6-2x.$$ Thus, $$A_3=\int_2^3 (6-2x)\,dx=\left[6x-x^2\right]_2^3=(18-9)-(12-4)=9-8=1.$$ 5. **Add all parts** $$\text{Total Area}=A_1+A_2+A_3=1+2+1=4.$$ 6. **Compare with the stored answer** Our derived answer is **4**, which corresponds to **Option B**.
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