Need help with a few problems

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sardion2000

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Jan 26, 2006
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Solve the system of equations for x and y.

-x + y = -8
4x +y = 7

Solve for a.
4(2a - 1) = -2(1 -5a)

Solve for x.
x + (1/3)x = 16

For the first one, is there any Tutorials on system of equations? I missed the class and my teacher will not go over it again for my benefit alone unfortunately and I cannot afford a tutor.

Let me explain just what confuses me. For the first one the entire thing is confusing, the second the paranthesis are twisting my brain into knots and the third it's the fraction thats getting me. :x

Any help would be great thanks in advance.
 
sardion2000 said:
Solve the system of equations for x and y.

-x + y = -8
4x +y = 7

Solve for a.
4(2a - 1) = -2(1 -5a)

Solve for x.
x + (1/3)x = 16

For the first one, is there any Tutorials on system of equations? I missed the class and my teacher will not go over it again for my benefit alone unfortunately and I cannot afford a tutor.

Any help would be great thanks in advance.
Click to expand...

You can use the addition or substitution method.

With the addition method multiply the first equation by -1, add like terms ( y disappears) and solve for x.

-x + y = -8
4x +y = 7

With the second method, solve one equation for y and substitute for y in the other equation. Then solve for x.
 
-x + y = -8
4x +y = 7
Two ways
y=x-8
Substitute
4x+x-8=7
5x=15
x=3
Or
subtract the first fron the second
5x=15
x=3
Plug that into either equation
4*(3)+y=7
y=7-12
y=-5

Solve for a.
4(2a - 1) = -2(1 -5a)
Multiply both terms inside the ()s by what is in front.
8a-4=-2+10a
Collect terms
-4+2=10a-8a
2a=-2
a=-1

Solve for x.
x + (1/3)x = 16
Multiply by 3
3x+x=48
4x=48
x=12

You can always check your answers by back-substitution.
In the first:
-x + y = -8
4x +y = 7
-(3)+(-5)=-8
4(3)+(-5)=7
 
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