Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Application of Integration question

2011 · Shift 1 · Q35
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Advanced
  3. /Mathematics
  4. /Application of Integration
  5. /2011 · Shift 1 · Q35

Application of Integration question

2011 · Shift 1 · Q35

JEE AdvancedMathematicsApplication of IntegrationMCQ+4 / −1
Let the straight line x=bx=bx=b divide the area enclosed by y=(1−x)2,y=0,y = {\left( {1 - x} \right)^2},y = 0,y=(1−x)2,y=0, and x=0x=0x=0 into two parts R1(0≤x≤b){R_1}\left( {0 \le x \le b} \right)R1​(0≤x≤b) and R2(b≤x≤1){R_2}\left( {b \le x \le 1} \right)R2​(b≤x≤1) such that R1−R2=14.{R_1} - {R_2} = {1 \over 4}.R1​−R2​=41​. Then bbb equals
  1. A
    34{3 \over 4}43​
  2. B
    12{ 1\over 2}21​
  3. C
    13{1 \over 3}31​
  4. D
    14{1 \over 4}41​
View written solutionFree

Correct answer: B

Step-by-step Solution:

  1. Understand the Geometry of the Area The problem describes the area enclosed by the parabola y=(1−x)2y = (1-x)^2y=(1−x)2, the x-axis (y=0y=0y=0), and the y-axis (x=0x=0x=0). The parabola y=(1−x)2y = (1-x)^2y=(1−x)2 has its vertex at (1,0)(1, 0)(1,0) and opens upwards. It intersects the y-axis at (0,1)(0, 1)(0,1). The enclosed area is under the curve from x=0x=0x=0 to x=1x=1x=1.

  2. Calculate the Total Area Let AAA be the total area enclosed by the curves. We can calculate this using a definite integral: A=∫01y dx=∫01(1−x)2 dxA = \int_{0}^{1} y \,dx = \int_{0}^{1} (1-x)^2 \,dxA=∫01​ydx=∫01​(1−x)2dx To evaluate the integral, we can use the power rule. Let u=1−xu = 1-xu=1−x, so du=−dxdu = -dxdu=−dx. The limits of integration change from x=0→u=1x=0 \to u=1x=0→u=1 and x=1→u=0x=1 \to u=0x=1→u=0. A=∫10u2(−du)=∫01u2 du=[u33]01=133−033=13A = \int_{1}^{0} u^2 (-du) = \int_{0}^{1} u^2 \,du = \left[ \frac{u^3}{3} \right]_0^1 = \frac{1^3}{3} - \frac{0^3}{3} = \frac{1}{3}A=∫10​u2(−du)=∫01​u2du=[3u3​]01​=313​−303​=31​ Alternatively, without substitution: A=[−(1−x)33]01=(−(1−1)33)−(−(1−0)33)=0−(−13)=13A = \left[ -\frac{(1-x)^3}{3} \right]_0^1 = \left( -\frac{(1-1)^3}{3} \right) - \left( -\frac{(1-0)^3}{3} \right) = 0 - \left( -\frac{1}{3} \right) = \frac{1}{3}A=[−3(1−x)3​]01​=(−3(1−1)3​)−(−3(1−0)3​)=0−(−31​)=31​ So, the total area is 13\frac{1}{3}31​.

  3. Define the Sub-regions R₁ and R₂ A vertical line x=bx=bx=b divides the total area into two parts:

    • R1R_1R1​ is the area from x=0x=0x=0 to x=bx=bx=b: R1=∫0b(1−x)2 dxR_1 = \int_{0}^{b} (1-x)^2 \,dxR1​=∫0b​(1−x)2dx
    • R2R_2R2​ is the area from x=bx=bx=b to x=1x=1x=1: R2=∫b1(1−x)2 dxR_2 = \int_{b}^{1} (1-x)^2 \,dxR2​=∫b1​(1−x)2dx The sum of these two areas must be the total area: R1+R2=A=13R_1 + R_2 = A = \frac{1}{3}R1​+R2​=A=31​.
  4. Use the Given Condition to Solve for b We are given the condition R1−R2=14R_1 - R_2 = \frac{1}{4}R1​−R2​=41​. We now have a system of two linear equations for R1R_1R1​ and R2R_2R2​:

    1. R1+R2=13R_1 + R_2 = \frac{1}{3}R1​+R2​=31​
    2. R1−R2=14R_1 - R_2 = \frac{1}{4}R1​−R2​=41​

    Adding the two equations eliminates R2R_2R2​: (R1+R2)+(R1−R2)=13+14(R_1 + R_2) + (R_1 - R_2) = \frac{1}{3} + \frac{1}{4}(R1​+R2​)+(R1​−R2​)=31​+41​ 2R1=4+312=7122R_1 = \frac{4+3}{12} = \frac{7}{12}2R1​=124+3​=127​ R1=724R_1 = \frac{7}{24}R1​=247​

  5. Calculate R₁ in terms of b and Solve for b Now we evaluate the integral for R1R_1R1​: R1=∫0b(1−x)2 dx=[−(1−x)33]0bR_1 = \int_{0}^{b} (1-x)^2 \,dx = \left[ -\frac{(1-x)^3}{3} \right]_0^bR1​=∫0b​(1−x)2dx=[−3(1−x)3​]0b​ R1=(−(1−b)33)−(−(1−0)33)=−(1−b)33+13R_1 = \left( -\frac{(1-b)^3}{3} \right) - \left( -\frac{(1-0)^3}{3} \right) = -\frac{(1-b)^3}{3} + \frac{1}{3}R1​=(−3(1−b)3​)−(−3(1−0)3​)=−3(1−b)3​+31​

    We equate this expression for R1R_1R1​ with the value we found in the previous step: 1−(1−b)33=724\frac{1 - (1-b)^3}{3} = \frac{7}{24}31−(1−b)3​=247​ Multiply both sides by 24: 8(1−(1−b)3)=78(1 - (1-b)^3) = 78(1−(1−b)3)=7 8−8(1−b)3=78 - 8(1-b)^3 = 78−8(1−b)3=7 8(1−b)3=8−7=18(1-b)^3 = 8 - 7 = 18(1−b)3=8−7=1 (1−b)3=18(1-b)^3 = \frac{1}{8}(1−b)3=81​ Take the cube root of both sides: 1−b=183=121-b = \sqrt[3]{\frac{1}{8}} = \frac{1}{2}1−b=381​​=21​ b=1−12=12b = 1 - \frac{1}{2} = \frac{1}{2}b=1−21​=21​

  6. Conclusion The value of bbb is 12\frac{1}{2}21​. This corresponds to option B.

PreviousNext

More from Application of Integration

  • Let f : [−1,2]→[0,∞] be a continuous function such that f(x)=f(1−x) for all x∈[−1,2] Let R1​=−1∫2​xf(x)dx,…2011 · MCQ
  • Let f be a real-valued function defined on the interval (0,∞) by f(x)=lnx+0∫x​1+sint​dt. then which of the following statement(s) is (are) true?2010 · Multiple correct
  • Consider the polynomial f(x)=1+2x+3x2+4x3. Let s be the sum of all distinct real roots of f(x) and let t=∣s∣. The area bounded by the curve y=f(x) and the lines x=0,y=0 and x=t,…2010 · MCQ
  • Area of the region bounded by the curve y=ex and lines x=0 and y=e is2009 · Multiple correct
  • Let f be a non-negative function defined on the interval [0,1]. If 0∫x​1−(f′(t))2dt​=0∫x​f(t)dt,0≤x≤1, and f(0)=0, then2009 · MCQ
  • Consider the functions defined implicitly by the equation y3−3y+x=0 on various intervals in the real line. If x∈(−∞,−2)∪(2,∞), the equation implicitly defines a unique real valued differentiable function y=f(x). If x∈(−2,2)…2008 · MCQ
  • The area of the region between the curves y=cosx1+sinx​​ and y=cosx1−sinx​​ bounded by the lines x=0 and x=4π​ is2008 · MCQ
  • Let ℝ denote the set of all real numbers. Then the area of the region $ \left\{ (x, y) \in \mathbb{R} \times \mathbb{R} : x > 0, y > \frac{1}{x}, 5x - 4y - 1 > 0, 4x + 4y - 17 is2025 · MCQ