How do I write an equation in slope-intercept form for the line- x-intercept (-9,0), y-intercept (0,7)

Question

write an equation in slope-intercept form for the line described.

x-intercept (-9,0), y-intercept (0,7)

Is it y=7/9x+7????

Answer 1

Slope-Intercept format is y = mx + b

To solve for m and b, you need 2 equations. We get that by using the two given points:

Using (-9,0):

0 = m(-9) + b (equation 1)

Using (0,7):

7 = m(0) = b (equation 2)

From #2, b=7

substitute that in #1 to get m = 7/9

So---- y = 7x/9 + 7

You got it right!!

Answer 2

Hi Brenda,

To get a line equation from two points, you'd need to first use these to find what the slope of the line is. Remember that y-mx+b, where m is the slope and b is the y intercept, is what we mean by this form. It's easiest to find the m, the slope, first.

How do we do that? With two points, the slope is the RISE/RUN, or (y_{2 –} y₁) ⁄ (x_{2 –} x₁). Here, you are correct. That is 7/9.

Great, so that's our m.

Then we need to know the y intercept. What's that? b, where x is 0. What's nice is that we already have it with one of the points. The y intercept is 7.

So your equation is correct.

If you didn't have that nice coincidence, you could plug in a point.

We know

y=7/9x+b, and that goes through point (-9,0)

so 0 = 7/9 (-9) + b

or 0 = -7 + b

b=7

Let me know if you have any questions!