Area Between 2 Curves and Finding Tangent Parabola Translation Constant

**kwikness** · July 11th 2011, 05:19 PM

Hi guys, I'm having trouble with this word problem. I can figure out how to find the area (part b) once I determine what interval I'm integrating over, but I'm not sure about how to find the interval, or find k where the parabola is tangent to y1.

Thanks.

**abhishekkgp** · July 11th 2011, 05:52 PM

Originally Posted by kwikness

Hi guys, I'm having trouble with this word problem. I can figure out how to find the area (part b) once I determine what interval I'm integrating over, but I'm not sure about how to find the interval, or find k where the parabola is tangent to y1.

Thanks.

let y=mx be tangent to the parabola. let the equation of the parabola be y=f(x). then the line cuts the parabola at only one point, that is, mx=f(x) has only one root. just do the discriminant=0 thingy.

**earboth** · July 11th 2011, 10:55 PM

Originally Posted by kwikness

Hi guys, I'm having trouble with this word problem. I can figure out how to find the area (part b) once I determine what interval I'm integrating over, but I'm not sure about how to find the interval, or find k where the parabola is tangent to y1.

Thanks.

1. If the curves of $y_1$ and $y_2$ are tangent then they must have the same gradient:

$|y_1'| = \left|\dfrac{dy_1}{dx} \right| = 1$

and

$y_2' = 0.16x$

2. Taking the right branch of $y_1$ you have to solve for x:

$0.16x = 1~\implies~x= \frac{25}4$

3. Therefore the tangent point is $T\left( \frac{25}4 , \frac{25}4 \right)$

4. Now determine the interval of the integration part (I would use some symmetry properties of the curves to simplify the calculations)

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