Question 595454
Write in slope-intercept form the equation of the line that passes through the given points. 
(-2,-8),(-1,0)

Hi, there!
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A linear equation in slope-intercept form is written as y = mx + b, where m is the slope and b is the y-intercept. Here, you have two points on the line, but you need to find the slope and the y-intercept.
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[I] Find the slope of the line. 
The definition of the slope is the change in y over the change in x. So, we find the difference between the y-values in the two points, the difference in the x-values, and then divide.
{{{m=(-8-0)/(-2-(-1))}}}
{{{m=(-8)/(-1)}}}
{{{m=8}}}
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Now we know that the slope of the line m is 8. We can substitute 8 for m in the slope-intercept equation.
{{{y=mx+b}}}
{{{y=8x+b}}}
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[II] Find the y-intercept.
Since both the points on the line make the equation true, we can substitute the x- and y-values for one of the points into the equation and solve for b. You can use either one. I'll use (-1,0).
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{{{y=8x+b)}}}
{{{0=(8)(-1)+b}}}
{{{0=-8+b)}}}
{{{8=b}}}
{{{b=8}}}
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The y-intercept for this equation is 8. Substitute 8 for b in the slope intercept equation.
{{{y=8x+b}}}
{{{y=8x+8}}}
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[III] Check your answer.
It's always a good idea to check your work. We need to make sure that both points are solutions for this equation. We substitute the x- and y-values into the equation.
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Check (-2,-8).
{{{y=8x+8}}}
{{{-8=8(-2)+8}}}
{{{-8=-16+8}}}
{{{-8=-8}}}
Bingo!!!
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Check (-1,0).
{{{y=8x+8}}}
{{{0=8(-1)+8}}}
{{{0=-8+8}}}
{{{0=0}}}
Winner, winner, chicken dinner!!!
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That's it. The equation of the line that passes through(-2,-8),(-1,0) is y=8x+8.
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Feel free to email me if you have questions about my explanation.
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Mrs.Figgy
math.in.the.vortex@gmail.com