Solve for a
a=\frac{b}{2}
Solve for b
b=2a
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a-b+a=0
Add a to both sides.
2a-b=0
Combine a and a to get 2a.
2a=b
Add b to both sides. Anything plus zero gives itself.
\frac{2a}{2}=\frac{b}{2}
Divide both sides by 2.
a=\frac{b}{2}
Dividing by 2 undoes the multiplication by 2.
-b=-a-a
Subtract a from both sides.
-b=-2a
Combine -a and -a to get -2a.
\frac{-b}{-1}=-\frac{2a}{-1}
Divide both sides by -1.
b=-\frac{2a}{-1}
Dividing by -1 undoes the multiplication by -1.
b=2a
Divide -2a by -1.
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