PrepRung

JEE Advanced 2019 Paper 2 · Mathematics · Area Under Curves · medium

Let R be the region \(x,y): |x^2-4|≤ y≤ 5\. The area of R is ______.

Numerical answer

Let RR be the region {(x,y): ∣x2−4∣≤y≤5}\{(x,y):\ |x^2-4|\le y\le 5\}. The area of RR is ______. (Give the answer correct to two decimal places.)
Show answer and solution

Answer: 14.67

The curve y=∣x2−4∣y=|x^2-4| equals 4−x24-x^2 for ∣x∣≤2|x|\le2 and x2−4x^2-4 for ∣x∣≥2|x|\ge2. It meets the line y=5y=5 where x2−4=5x^2-4=5, i.e. x=±3x=\pm3 (the branch 4−x24-x^2 never reaches 55). So RR lies between x=−3x=-3 and x=3x=3 with upper boundary y=5y=5. By symmetry about the yy-axis, area =2[∫02(5−(4−x2))dx+∫23(5−(x2−4))dx]=2[∫02(1+x2) dx+∫23(9−x2) dx]=2\left[\int_0^2\left(5-(4-x^2)\right)dx+\int_2^3\left(5-(x^2-4)\right)dx\right]=2\left[\int_0^2(1+x^2)\,dx+\int_2^3(9-x^2)\,dx\right]. The first integral is 2+83=1432+\frac83=\frac{14}3; the second is 9−27−83=839-\frac{27-8}{3}=\frac{8}3. Hence the area is 2(143+83)=443≈14.6672\left(\frac{14}3+\frac83\right)=\frac{44}3\approx14.667, i.e. 14.6714.67. Computing the area as a rectangle minus the region under the curve gives 30−463=44330-\frac{46}3=\frac{44}3 as a check.
Report a mistake

Original question written in the JEE Advanced 2019 Paper 2 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake