Verified Solution • 2025–26 Session moderate

QJEEM24Mae8a7: JEE Main 2024 Mathematics - Class 12 JEEM24Mae8a7 Solution: Let β ( m , n ) = ∫ 0 1 x m − 1 ( 1 − x ) n − 1   d x ,…

Let β(m,n)=∫01xm−1(1−x)n−1 dx, m,n>0. If ∫01(1−x10)20 dx=a×β(b,c), then 100(a+b+c)100(\mathrm{a}+\mathrm{b}+\mathrm{c}) equals _________.

Multiple Choice Options

  • A 2012
  • B 1021
  • C 1120
  • D 2120

Step-by-Step Verified Solution

First, let's rewrite the given integral using the given form of the Beta function. The given integral is:

∫01(1−x10)20 dx

To use the Beta function, let us make a substitution. Let x10=tx^{10} = t . Then, dx=110t−910dtdx = \frac{1}{10}t^{-\frac{9}{10}} dt or dx=110t−910dtdx = \frac{1}{10} t^{-\frac{9}{10}} dt . The limits of integration change as follows: when x=0x = 0 , t=0t = 0 , and when x=1x = 1 , t=1t = 1 .

Substituting these into the integral, we have:

∫01(1−t)20⋅110t−910dt

which simplifies to:

110∫01(1−t)20t−910dt

We recognize this integral as a Beta function β(m,n)\beta(m, n) where m=1−910=110m = 1 - \frac{9}{10} = \frac{1}{10} and n=20+1=21n = 20 + 1 = 21 .

Therefore, we can write this as:

110β(110,21)\frac{1}{10} \beta \left( \frac{1}{10}, 21 \right)

Comparing this to a×β(b,c)a \times \beta(b, c) , we have a=110a = \frac{1}{10} , b=110b = \frac{1}{10} , and c=21c = 21 .

Now we calculate 100(a+b+c)100(a + b + c) :

100(110+110+21)=100(110+110+21)=100(15+21)=100(15+1055)=100(1065)=100×21.2=2120100 \left( \frac{1}{10} + \frac{1}{10} + 21 \right) = 100 \left( \frac{1}{10} + \frac{1}{10} + 21 \right) = 100 \left( \frac{1}{5} + 21 \right) = 100 \left( \frac{1}{5} + \frac{105}{5} \right) = 100 \left( \frac{106}{5} \right) = 100 \times 21.2 = 2120

So, the answer is Option D, 2120.

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