Find the number a such that the line x = a bisects the area under the curve y = 1/x2 for 1 ≤ x ≤ 4.
Find the number b such that the line y = b bisects the area in part (a).
Solution:
Given, y = 1/x2 for 1 ≤ x ≤ 4.
1) we have to find a such that the line x = a bisects the area under the given curve for 1 ≤ x ≤ 4.
So, \(\int_{1}^{a}\frac{dx}{x^{2}}=\int_{a}^{4}\frac{dx}{x^{2}}\)
\(\left [ \frac{-1}{x} \right ]_{1}^{a}=\left [ \frac{-1}{x} \right ]_{a}^{4}\)
\(\\(\frac{-1}{a})-(\frac{-1}{1})=(\frac{-1}{4})-(\frac{-1}{a})\\(\frac{-1}{a})+1=(\frac{-1}{4})+(\frac{1}{a})\\(\frac{1}{a})+(\frac{1}{a})=1+\frac{1}{4}\\\frac{2}{a}=\frac{5}{4}\)
5a = 8
a = 8/5
2) Integrating with respect to y will make things easier.
y = 1/x2
x2 = 1/y
x = ±1/√y
We know, x > 0 so take positive square root
x = 1/√y
Now we want to find b,
\(\int_{0}^{b}\frac{dy}{\sqrt{y}}=\int_{b}^{1}\frac{dy}{\sqrt{y}}\)
\(\\\left [ 2\sqrt{y}\right ]_{0}^{b}=\left [ 2\sqrt{y}\right ]_{b}^{1}\\2(\sqrt{b}-0)=2(1-\sqrt{b})\\2\sqrt{b}=2-2\sqrt{b}\\\sqrt{b}=1-\sqrt{b}\\2\sqrt{\sqrt{b}}=1\\\sqrt{b}=\frac{1}{2}\)
Squaring on both sides,
b = 1/4
Therefore, the values of a and b are 8/5 and 1/4.
Find the number a such that the line x = a bisects the area under the curve y = 1/x2 for 1 ≤ x ≤ 4.
Find the number b such that the line y = b bisects the area in part (a).
Summary:
The number a such that the line x = a bisects the area under the curve y = 1/x2 for 1 ≤ x ≤ 4 is 8/5. The number b such that the line y = b bisects the area in part (a) is 1/4.
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