Question Details

You may not know integration. But using dimensional analysis you can check on some results. In the integral ∫ dx/(2ax-x²)⁰.⁵ = aⁿ sin⁻¹((x/a)-1) the value of n is

Options

A

1

B

-1

C

0

D

1/2

Correct Answer :

0

Solution :

The correct option is 0.

Let us analyze the dimensions of both sides of the given equation to find the value of n using dimensional analysis.

The given equation is:
��dx(2ax-x2)0.5=ansin-1(xa-1)

Here, x represents a position or distance, which has the dimension of length, denoted as:
[x]=L

Since dx is an infinitesimal change in x, its dimension is also:
[dx]=L

In the term 2ax-x2, we are subtracting x2 from 2ax. For this subtraction to be dimensionally valid, both terms must have the same dimensions. Since [x2]=L2, the term 2ax must also have the dimension of L2:
[2ax]=[a][x]=[a]L=L2
This gives the dimension of the constant a as:
[a]=L

Now, let us determine the dimensions of the Left-Hand Side (LHS) of the equation:
[LHS]=[dx(2ax-x2)0.5]
The integration symbol acts as a summation and does not change the overall dimensions. Thus:
[LHS]=[dx][2ax-x2]0.5=L(L2)0.5=LL=L0
So, the LHS is a dimensionless quantity (dimension L0).

Next, let us analyze the Right-Hand Side (RHS) of the equation:
[RHS]=[ansin-1(xa-1)]
Trigonometric functions and inverse trigonometric functions (like sin-1θ) represent angles and are dimensionless. Therefore:
[sin-1(xa-1)]=L0
Consequently, the dimension of the RHS is determined solely by an:
[RHS]=[a]n=Ln

For the equation to be dimensionally correct, the dimensions of the LHS and RHS must be equal:
[LHS]=[RHS]
L0=Ln

Comparing the exponents of L on both sides, we get:
n=0

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