Posted by **Lilly** on Monday, November 30, 2009 at 6:04pm.

Write an equation in a standard form of the line that passes thru (3,1) and has a y-intercept of-2 .

My book does not have problems like this so PLEASE help me!!!!!!!!!

- Math -
**Reiny**, Monday, November 30, 2009 at 6:31pm
given the y-intercept of -2 implies you have a second point (0,-2)

so the slope is (-2-1)/(0-3) = -3/-3 = 1

You now have the slope and the y-intercept.

Can you take it from here ?

- Math -
**Lilly**, Monday, November 30, 2009 at 6:33pm
x+y=-2 ?

- Math -
**Reiny**, Monday, November 30, 2009 at 6:38pm
very close.

from the information so far we would have

y = x - 2

or x - y = 2

You can always check if your equation is correct by subbing in the given points.

notice for your equation and using (3,1)

we would get

3+1 = 2 ??

- Math -
**Lilly**, Monday, November 30, 2009 at 6:40pm
How would you get a positive 2 though?

- Math -
**Reiny**, Monday, November 30, 2009 at 6:44pm
I had better put my glasses on.

I read your equation as x+y = 2, didn't notice the - sign in front.

Good observation!

- Math -
**Lilly**, Monday, November 30, 2009 at 6:46pm
thats ok, so would it be 4 ?

I now got -3x+y=-2

- Math -
**Reiny**, Monday, November 30, 2009 at 7:30pm
no, I thought you understood when I told you it was x-y = 2.

Let's try it again:

2 points

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

slope = (-2-1)/(0-3) = 1

then using y = mx + b

we have y = (1)x - 2

or -x + y = -2

or

x - y = 2

- Math -
**Anonymous**, Monday, November 30, 2009 at 8:01pm
ok thanks, sorry!

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