Posted by **kim** on Wednesday, September 23, 2009 at 7:05pm.

find an equation of the line that passes through the points

(0,0),(-1,5)

and

(2,1),(0,-3)

- pre calculus -
**DrBob222**, Wednesday, September 23, 2009 at 7:37pm
The first one is

slope = y1-y2/x1-x2

slope = m = (0-5/0+1 = -5

y = mx + b

Then put in one of the points to calculate b.

5 = -5(-1) + b

5 = 5 + b

b = 0

So the line is

y= mx + b

y = -5x + 0 or y = -5x.

The other one is don the same way.

Check my work very carefully.

- pre calculus -
**kim**, Wednesday, September 23, 2009 at 7:43pm
is the other problem is

y=-3x+0

- pre calculus -
**jim**, Wednesday, September 23, 2009 at 7:43pm
The first pair is very very easy.

Remember that a line that passes through the origin must be of the form:

y = mx

since the intercept is zero. You are told that this line passes through the origin and that the point (-1, 5) satisfies the equation. You should be able to write the answerdown from there.

There are a couple of ways to do the second one. he two-point formula is

(y - y1) / (x - x1) = (y2 - y1) / (x2 -x1)

(y - 1) / (x - 2) = (-3 - 1) / (0 - 2)

(y - 1) / (x - 2) = 2

multiply across by x - 2

y -1 = 2x - 4

and you should be close enough to finish from there.

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