SOLUTION: Solve the following system of linear equations using the substitution method: {{{(-1/4)x + (3/2)y = 11}}} {{{(-1/8)x + (1/3)y = 3}}} Express answer as an ordered pair.

Algebra ->  Finance -> SOLUTION: Solve the following system of linear equations using the substitution method: {{{(-1/4)x + (3/2)y = 11}}} {{{(-1/8)x + (1/3)y = 3}}} Express answer as an ordered pair.       Log On


   



Question 1108482: Solve the following system of linear equations using the substitution method:
%28-1%2F4%29x+%2B+%283%2F2%29y+=+11
%28-1%2F8%29x+%2B+%281%2F3%29y+=+3
Express answer as an ordered pair.

Found 2 solutions by asymptote, TeachMath:
Answer by asymptote(2) About Me  (Show Source):
You can put this solution on YOUR website!
Solve for y in the first equation, then plug this expression into the second equation and solve for x:
1) Add x term to both sides: %283%2F2%29y+=+11+%2B+%281%2F4%29x
2) Divide both sides by 3/2 (a.k.a multiply by reciprocal, 2/3) to isolate y: y+=+%2822%2F3%29+%2B+%281%2F6%29%2Ax
3) Now substitute this expression for y in the second equation:
%28-1%2F8%29%2Ax+%2B+%281%2F3%29%2A%28%2822%2F3%29+%2B+%281%2F6%29%2Ax%29+=+3
4) Simplify left-hand side by distributing 1/3 in preparation of isolating x:
%28-1%2F8%29%2Ax+%2B+%2822%2F9%29+%2B+%281%2F18%29%2Ax+=+3
5) Combine x terms by using common denominator of 72:
%28-5%2F72%29%2Ax+%2B+%2822%2F9%29+=+3
6) Subtract 22/9 from both sides by using common denominator of 9:
%28-5%2F72%29%2Ax+=+%285%2F9%29
7) Solve for x by multiplying both sides by -72/5 (a.k.a dividing by -5/72):
x+=+-8
We now know x and can plug -8 into either of the original two equations and solve for y. I will use the second equation:
1) %28-1%2F8%29%2A-8+%2B+%281%2F3%29%2Ay+=+3
2) 1+%2B+%281%2F3%29%2Ay+=+3
3) %281%2F3%29%2Ay+=+2
4) y+=+6
When we plug x = -8 and y = 6 back into both original equations, we get true equalities, verifying our answer.
Finally, writing as ordered pair, (x,y) yields (-8, 6) as our final answer.
Just as a note, unless you had to solve this by substitution, I would recommend using the elimination method as it would be much quicker.


Answer by TeachMath(96) About Me  (Show Source):
You can put this solution on YOUR website!
– ¼x + (3/2)y = 11
(– 1/8)x + (1/3)y = 3
Multiply eq 1 by - 4 to get: x - 6y = - 44____x = 6y - 44
Multiply eq 2 by LCD, 24 to get: - 3x + 8y = 72
Then substitute 6y - 44 for x in the equation: - 3x + 8y = 72
This should give you a y-value of 6
Substitute 6 for y in any of the 2 original equations to get an x-value of - 8.