To solve the equation \(\sqrt{4x - 3} = 9\), we can follow these steps:
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Square both sides to eliminate the square root:
\[ (\sqrt{4x - 3})^2 = 9^2 \]
This simplifies to:
\[ 4x - 3 = 81 \]
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Add 3 to both sides:
\[ 4x = 81 + 3 \] \[ 4x = 84 \]
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Divide both sides by 4:
\[ x = \frac{84}{4} \] \[ x = 21 \]
Now, let's verify the solution by substituting \(x = 21\) back into the original equation:
\[ \sqrt{4(21) - 3} = \sqrt{84 - 3} = \sqrt{81} = 9 \]
Since both sides of the original equation are equal, the solution \(x = 21\) is correct.
Thus, the solution is:
\[ \boxed{21} \]