# pre calculus

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find an equation of the line that passes through the points

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

and

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

• pre calculus -

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 -

is the other problem is

y=-3x+0

• pre calculus -

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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