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Question 969411: Complete the equation for the linear function whose graph contains the point (7,8) and has a slope of -1.2
I need to understand how to work this problem to help my child with her math.
Found 2 solutions by Boreal, stanbon:
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! This requires the point slope formula or just substituting.
Let's do the point slope first
y-y1=m(x-x1) y1 is the y value of the ordered pair and x1 is the x value. m is the slope
y-8=1.2(x-7) Be careful with the signs. If the y value were -8, the left side would be y- -8 or y+8
Now distribute
y-8=(1.2*x) -8.4 (1.2*7)
add 8 to both sides
y=1.2x -0.4 That is the equation of the line.
This way below may be easier.
y=mx +b
Plug is x,y, and m
8=1.2(7) +b
8=8.4 +b
subtract 8.4 from both sides
b=(-0.4)
y=1.2x - 0.4
This is the same answer and should serve as a check. If you have two ordered pairs and they ask for the equation of the line, figure the slope and then use EITHER ordered pair to finish the job. You will get the same result for each ordered pair, and you may use that to check.
Hope that helps.
Answer by stanbon(75887)  (Show Source):
You can put this solution on YOUR website! Complete the equation for the linear function whose graph contains the point (7,8) and has a slope of -1.2
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Form of the equation: y = mx + b
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You are given that y = 8 when x = 7.
And you are given that m = -1.2
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Substitute for those letters and solve for "b"::
8 = -1.2*7 + b
8 = -8.4 + b
b = 8 + 8.4 = 16.4
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The answer you want is::
y = -1.2x + 16.4
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Hope that helps.
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If your son/daughter says "That is not the
way we do it in class", let me know, as there
are several methods being taught these days.
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Cheers,
Stan H.
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