Question 123790
A line passing through (–6, –5) and (–1, y) is perpendicular to a line with slope -5/13 . Find the value of y 
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It's useful to remember that the relationship of slopes of perpendicular lines is:
m1 * m2 = -1
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Let m1 = -5/3, the given slope
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m2 = slope of given coordinates line
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Find m2
(-5/3)*m2 = -1
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m2 = -1 * (-3/5); (invert and multiply dividing fractions)
m2 = +3/5
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Using the slope formula: {{{(y2-y1)/(x2-x1)}}} = m
Assign the given coordinates: x1=-6, y1=-5; x2=-1; y2=y
{{{(y -(-5))/(-1-(-6)) = 3/5}}} 
{{{(y + 5)/(-1 + 6) = 3/5}}} 
{{{((y+5))/5 = 3/5}}}
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Both have the same denominators so we can say:
y + 5 = 3
y = 3 - 5
y = -2
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Check using the slope formula with y=-2
{{{(-2 -(-5))/(-1-(-6)) = 3/5}}}
{{{(-2 + 5)/(-1 + 6) = 3/5}}} confirms our solution