SOLUTION: If the line passing through the points (1, a) and (4, -2) is parallel to the line passing through the points (2, 8) and (-7, a + 4), what is the value of a? Thanks for your he

Algebra ->  Linear-equations -> SOLUTION: If the line passing through the points (1, a) and (4, -2) is parallel to the line passing through the points (2, 8) and (-7, a + 4), what is the value of a? Thanks for your he      Log On


   

Question 646777: If the line passing through the points (1, a) and (4, -2) is parallel to the line passing through the points (2, 8) and (-7, a + 4), what is the value of a?

Thanks for your help.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

parellel lines have identical slopes

(1, a) and 

(4, -2) m+=+%28a%2B2%29%2F%28-3%29



(2, 8) and 

(-7, a + 4)  m+=+%288+-%28a%2B4%29%29%2F9



%28a%2B2%29%2F%28-3%29+=+%288+-%28a%2B4%29%29%2F9 |Multiplying thru by 9 so as all denominators = 1

-3(a+2) = 8-(a+4)

 -3a - 6 = 8 -a - 4

    -10 = 2a

    -5 = a

and...

(1, -5) and 

(4, -2) m = -3/-3 = 1

(2, 8) and 

(-7, -1) m = 9/9 = 1