Graphs/equations/point of intersection

• May 17th 2009, 10:31 AM
saran35
Graphs/equations/point of intersection
The solutions of the equation 2x + 2/x = 7 are the x-coordinates of the points of intersection of the graph of y = x + 2/x and a straight line L
Find the equation of L.
• May 17th 2009, 11:17 AM
VonNemo19
First find x in the first equation

$2x+\frac{2}{x}=7$

$x+\frac{1}{x}=\frac{7}{2}$

$\frac{x^2+1}{x}=\frac{7}{2}$

$x^2+1=\frac{7}{2}x$

$\frac{7}{2}x-\frac{2x^2}{2}=1$

$\frac{7x-2x^2}{2}=1$

$7x-2x^2=2$

$x^2-\frac{7}{2}x=-1$

$x^2-\frac{7}{2}x+\frac{49}{16}=1+\frac{49}{16}$

$(x-\frac{7}{4})^2=1+\frac{49}{16}$

$x-\frac{7}{4}=\pm{\sqrt{1+\frac{49}{16}}}$

$x=\pm{\sqrt{1+\frac{49}{16}}}+\frac{7}{4}$

So this particular value of x lies on the graph of the equation $y=x+\frac{2}{x}$ and is also a point on the line $L$.

Can you take it from here?

I'll give you a hint.

Plug the values $+{\sqrt{1+\frac{49}{16}}}+\frac{7}{4}$ and $-{\sqrt{1+\frac{49}{16}}}+\frac{7}{4}$ into the equation $y=x+\frac{2}{x}$. They are two points on L.
• May 18th 2009, 03:20 PM
mathswend
2x +2/x = 7
subtract x from both sides
x + 2/x = 7 - x

so you need to draw y = x + 2/x and the straight line y = 7 - x

It's as simple as that!!
• May 18th 2009, 05:03 PM
VonNemo19
yes