Question

How do you evaluate the definite integral `int (3x^2) dx` from `[1,2]`?

Answer 1

I found `7`

Explanation:

We first evaluate the indefinite integral to find the function called the Primitive; then we evaluate the primitive at the extremes and subtract the vales.
In your case we have:

`int_1^2(3x^2)dx=cancel(3)x^3/cancel(3)=x^3` which is the Primitive;

we now evaluate it at `2 and 1` and subtract the values obtained:

`(2^3)-(1^3)=8-1=7`