Help please!

**MathMack** · November 15th 2007, 05:35 PM

Consider the line that passes through the points (4,3) and -4,5

What is the slope of this line? also Write an equation in X and Y for this line. You do not have to simplify this equation or solve it.
last is to write an equation for the line that passes through the points 5,3 and 5,-2

Thanks in advance everyone!

**topsquark** · November 15th 2007, 06:01 PM

Originally Posted by MathMack

Consider the line that passes through the points (4,3) and -4,5

What is the slope of this line? also Write an equation in X and Y for this line. You do not have to simplify this equation or solve it.
last is to write an equation for the line that passes through the points 5,3 and 5,-2

Thanks in advance everyone!

Given two points $(x_1, y_1) \text{ and } (x_2, y_2)$ the slope of the line that passes through them is
$m = \frac{y_2 - y_1}{x_2 - x_1}$

The slope-intercept form of a line is
$y = mx + b$

So let's take your first pair of points:
$m = \frac{5 - 3}{-4 - 4} = \frac{2}{-8} = -\frac{1}{4}$

So the form for the line is:
$y = -\frac{1}{4}x + b$

We need to find b. So plug either point into this formula. I'll choose the first one:
$3 = -\frac{1}{4} \cdot 4 + b$

$3 = -1 + b$

$b = 4$

Thus your line equation is
$y = -\frac{1}{4}x + 4$

You can verify that the other point also satisfies this equation.

You do the other problem.

-Dan

**poofighter** · November 15th 2007, 06:03 PM

change in y/change in x = m(slope)
m=Y2-y1/x2-x1

**MathMack** · November 15th 2007, 07:28 PM

Hey guys thanks, i'm kinda lost on this part, "last is to write an equation for the line that passes through the points 5,3 and 5,-2"

**topsquark** · November 15th 2007, 07:50 PM

Originally Posted by MathMack

Hey guys thanks, i'm kinda lost on this part, "last is to write an equation for the line that passes through the points 5,3 and 5,-2"

Hint: What is the slope of this line? Does it exist? If not, what does that mean about the line?

-Dan

**MathMack** · November 15th 2007, 08:40 PM

For the 1st part I got y=1/4x+2

I did the y-y1=m(x-x1) which I figured and put in what I had, which is y-3=1/4(x-4) which then figures to y-3=1/4x-1 which figures to be y= -1/4x+2

I noticed you got y= -1/4x+4, where am I going wrong?

**MathMack** · November 15th 2007, 08:41 PM

nevermind figured where I went wrong, forgot a minus sign in there!

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