SOLUTION: -3x-2y=5.5 and x+3y=7.5 Solve Using substitution I got (4.5,4) but I thinks wrong when I check it. Please help!!!

Algebra ->  Expressions-with-variables -> SOLUTION: -3x-2y=5.5 and x+3y=7.5 Solve Using substitution I got (4.5,4) but I thinks wrong when I check it. Please help!!!      Log On


   

Question 403067: -3x-2y=5.5 and x+3y=7.5
Solve Using substitution
I got (4.5,4) but I thinks wrong when I check it. Please help!!!
Answer by rvquartz(19) About Me  (Show Source):
You can put this solution on YOUR website!
(a) -3x - 2y = 5.5
(b) x + 3y = 7.5
from (b), we have x = (7.5 - 3y)
substituting into (a), we have -3(7.5 - 3y) - 2y = 5.5
this is the same as
(-3)(7.5) - (-3)(3y) - 2y = 5.5
-22.5 + 9y - 2y = 5.5
{remember two 'negatives' equal 'positive' that is why we have +9y instead of -9y}
that is the same as
-22.5 +7y = 5.5
that is the same as
7y = 5.5 + 22.5 = 28;
so 7y = 28 and
y = 4
since x = (7.5 - 3y)
x = -4.5