# Determining x-intercepts of a curve

• March 16th 2009, 09:33 PM
Meeklo Braca
Determining x-intercepts of a curve
Hey guys and gals.

I was wondering if I could get some help with a question that reads.

Determine the x-intercepts of the curve which has a slope 2x +1 and passes through (1, -4)

Thank You so much!
• March 16th 2009, 11:06 PM
Prove It
Quote:

Originally Posted by Meeklo Braca
Hey guys and gals.

I was wondering if I could get some help with a question that reads.

Determine the x-intercepts of the curve which has a slope 2x +1 and passes through (1, -4)

Thank You so much!

If it has a slope of $2x + 1$ then we can say

$\frac{dy}{dx} = 2x + 1$.

Therefore

$y = \int{2x + 1\,dx}$

$y = x^2 + x + C$.

We're told that $(1, -4)$ lies on the curve, so

$-4 = 1^2 + 1 + C$

$-4 = 1 + 1 + C$

$-4 = 2 + C$

$-6 = C$.

Thus $y = x^2 + x - 6$.