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Let A and B be constants such that the graphs of the lines x + 5y  = 7 and 15x + Ay = B are perpendicular and intersect at (-8,3). Enter the ordered pair (A,B).

 Feb 23, 2020
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x + 5y  =7 

15x + Ay   = B

 

The slope of the first line =  -(1/5)

 

So..since the lines are perpendicular  ..the slope of the second line must  be    =  5

 

This implies that     -15/A = 5     ⇒  A  = -3

 

If the lines  intersect  at   (-8, 3)......the  for the second line, 

 15(-8) + -3(3)  = B

-120  - 9  = B

B  = -129

 

So the equation of the second line must   be

 

15x  - 3y  = -129

 

So   (A, B)  =  (-3 -129)

 

Here's a graph  : https://www.desmos.com/calculator/zyizjg9kkt

 

 

 

cool cool cool

 Feb 23, 2020

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