How to Find the Area Bounded by a Curve Using Integrals

Join the discussion
Registration is free. Start your own thread to ask a follow-up.
3 replies · 2K views · last reply
SherlockOhms
Messages
309
Reaction score
0
Find the area bound by the curve y = x^3 - 2x^2 - 5x + 6, the x-axis and the lines x = -1 and x = 2. The answer is 157/12.

The curve cuts the x-axis at x = -2, 1 and 3. I've shown my general idea on the attachment. I didn't end up with the correct answer so could somebody explain to me where I've gone wrong?
 
Physics news on Phys.org
Handwritten sketch of a cubic curve y = f(x) crossing the x-axis at x = -2, -1, 2 and 3, with shaded regions between the curve and the axis; below it, the antiderivative x^4/4 - 2x^3/3 - 5x^2/2 + 6x and the split integral from -2 to -1 plus from -1 to 2 of y dx.
 
DAPOS said:
Find the area bound by the curve y = x^3 - 2x^2 - 5x + 6, the x-axis and the lines x = -1 and x = 2. The answer is 157/12.

The curve cuts the x-axis at x = -2, 1 and 3. I've shown my general idea on the attachment. I didn't end up with the correct answer so could somebody explain to me where I've gone wrong?
Your integral for the interval [1, 2] is not set up correctly. It should look like this:
$$\int_1^2 (0 - y)dx $$
Do you see why?

BTW, do not discard the three parts of the homework template. They are there for a reason.
 
Mark44 said:
Your integral for the interval [1, 2] is not set up correctly. It should look like this:
$$\int_1^2 (0 - y)dx $$
Do you see why?

BTW, do not discard the three parts of the homework template. They are there for a reason.

Thanks for that. The graph goes below the x-axis.
I sent that from my phone and the templates don't actually show for you to use.
Thanks again.