Solve for r
\left\{\begin{matrix}r=\frac{4y+9}{x}\text{, }&y\neq -\frac{9}{4}\text{ and }x\neq 0\\r\neq 0\text{, }&x=0\text{ and }y=-\frac{9}{4}\end{matrix}\right.
Solve for x
x=\frac{4y+9}{r}
r\neq 0
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xr=4y+9
Variable r cannot be equal to 0 since division by zero is not defined. Multiply both sides of the equation by r.
\frac{xr}{x}=\frac{4y+9}{x}
Divide both sides by x.
r=\frac{4y+9}{x}
Dividing by x undoes the multiplication by x.
r=\frac{4y+9}{x}\text{, }r\neq 0
Variable r cannot be equal to 0.
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