Question 519615
Your best chance of an answer is to ask one question at a time, not five. 
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1) m = change in y / change in x = rise over the run = (y-y<sub>1</sub>)/(x-x<sub>1</sub>)
m = (2-2)/(1-4) 
m = 0/-3 = 0 which is a horizontal line
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2) y = 2x -3
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3) See below.
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4) Vertical line through (7,-2) is x=7
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5) See below.
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3) slope and equation  of line through (-1,2) and (4,-1/2).
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m = 2-(-1/2) / -1-4
m = 2+1/2 / -5
m  = (5/2) / -5 = -1/2
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y = -1/2x + b
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use one of the known points to find 'b'
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2 = -1/2(-1) +b
2 = 1/2 +b 
b = 3/2
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y = -1/2x + 3/2
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y-intercept occurs where x=0, which is (0,3/2)
x-intercept occurs where y=0, which is (3,0)
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Graph to check
{{{ graph(500,500,-5,5,-5,5,-1/2*x+3/2) }}}
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5) Equation for the line through the point (5,7) with a slope of 2.
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y = 2x + b
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use the known point to find 'b'
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7 = 2(5) + b
7 = 10 + b
b = -3
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y = 2x-3
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y-intercept = (0, -3)
x-intercept = (3/2, 0)
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Graph
{{{ graph(500,500,-10,10,-10,10,2*x-3) }}}