SOLUTION: Use substitution to solve the linear system. x + 4y = 21 4x + 2y = 6 AND Different problem: Find the solution to the system by graphing. x + y = 6 4x - y = 7

Algebra ->  Algebra  -> Coordinate Systems and Linear Equations  -> Lessons  -> Linear Equations Lesson -> SOLUTION: Use substitution to solve the linear system. x + 4y = 21 4x + 2y = 6 AND Different problem: Find the solution to the system by graphing. x + y = 6 4x - y = 7      Log On

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Question 27823: Use substitution to solve the linear system.
x + 4y = 21
4x + 2y = 6
AND Different problem:
Find the solution to the system by graphing.
x + y = 6
4x - y = 7
Answer by bmauger(101) About Me  (Show Source):
You can put this solution on YOUR website!
x%2B4y=21Subtract 4y from both sides:
x=21-4yNow use 21-4y to substitute for x in the second equation:
4x%2B2y=6
4%2821-4y%29%2B2y=6Distribute:
84-16y%2B2y=6Rearrange:
-14y=-78Divide:
y=14%2F78
y=7%2F39
x=21-4%287%2F39%29
x=791%2F39%29
Problem 2:
graph+%28300%2C+300%2C+-3%2C+8%2C+-3%2C+8%2C%0D%0A6-x%2C%0D%0A4x-7%29
Graphically it looks like: (2.5, 3.5) or x=2.5 & y=3.5
Checking 2.5%2B3.5=6 Check.
4%282.5%29-3.5=6.5 Pretty close... close as you should expect to get finding the answer through graphing.