SOLUTION: 4x-y=5 4x+4y=-4 solve the linear system using subtraction

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Question 982010: 4x-y=5 4x+4y=-4 solve the linear system using subtraction
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
4x-y=5......eq.1
4x%2B4y=-4+......eq.2
------------------------------subtract eq.2 from eq.1
4x-y-%284x%2B4y%29=5-%28-4%29
cross%284x%29-y-cross%284x%29-4y=5%2B4
-y-4y=9
-5y=9
y=9%2F-5


find x
4x-%28-9%2F5%29=5......eq.1
4x%2B9%2F5=5
4x=5-9%2F5
4x=25%2F5-9%2F5
4x=16%2F5
x=%28cross%2816%294%2F5%29%2Fcross%284%29
x=4%2F5


Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!

You have a linear system of two equations in two unknowns

system%284x-y=5%2C+%0D%0A4x%2B4y=-4%29.

Subtract the second equation from the first one.  You will get a single equation in one unknown

-y - 4y = 5 - (-4),   or

-5y = 5 + 4,  or

5y = -9.

Hence,  y = -9%2F5 = -1.8.

Now,  substitute this value of  y  into the first equation of the original system.  You will have

4x - (-1.8) = 5,

4x = 5 - 1.8,

4x = 3.2,

x = 3.2%2F4 = 0.8.

Answer.  x = 0.8, y = -1.8.