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MHT CET · Maths · Definite Integration

If \(\int_a^b x^3 d x=0\) and if \(\int_a^b x^2 d x=\frac{2}{3}\), then \(a\) and \(b\) are respectively

  1. A \(1,-1\)
  2. B \(-1,-1\)
  3. C 1,1
  4. D -1,1
Verified Solution

Answer & Solution

Correct Answer

(D) -1,1

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \int_a^b x^3 d x=0 \text { and } \int_a^b x^2 d x=\frac{2}{3} \\ & \Rightarrow\left[\frac{x^4}{4}\right]_a^b=0 \text { and }\left[\frac{x^3}{3}\right]_a^b=\frac{2}{3} \\ & \Rightarrow \frac{b^4}{4}-\frac{a^4}{4}=0 \text { and } \frac{b^3}{3}-\frac{a^3}{3}=\frac{2}{3} \\ & \Rightarrow a^4=b^4 \text { and } b^3-a^3=2\end{aligned}\)
which is satisfied by \(\mathrm{a}=-1\) and \(\mathrm{b}=1\)