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Understanding IITJEE Integration: The Easy Way - 1

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Suppose you were told that a function had a gradient given by
Could you work out that function?

By referring back to differentiation, you would notice that this gradient was given by the function

 

 

 

 

Is this then our function?

Not necessarily! We would get the same gradient for the function

This process of finding the function from it's gradient, is called Integration.

This is only the most basic use of integration. Together with differentiation, it is probably the most important area of maths.

The basic method of integration, is to reverse differentiation.

To differentiate, we multiplied by the power, then subtracted 1 from the power

=>
To integrate, we reverse this exactly.

First add 1 to the power, then divide by the new power.

=>

Notice that there is a constant added onto the function. This is because, as in the case above, we do not know whether or not a number must be added to our function.

Example

Find the curve whose gradient is

Add 1 the power an divide by new power.
Simplify Important If you leave off the c, your answer is wrong and you will lose a mark

Clearly it is not very satisfactory to have these unknowns in our answers.

If we are told a point that the graph passes through, then we can evaluate the constant.

For example

A curve has a gradient function
and passes through the point

Find the equation of the curve

Add 1 to the power and divide by new power.
Simplify
Substitute in
So the curve is

What is the effect of integrating a constant? We can say this because anything to the power 0 is equal to 1
The power of x now becomes 1
Suppose that
Which gives When you integrate a constant, you just put an x behind the constant.

The problem case
What happens if you integrate?
The power goes to nought, so we get Not allowed!
We can however integrate x-1
Remember from differentiation that if
then
Since integration is just the reverse of differentiation, this is our answer.
If
say x=1 when y=2

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