To evaluate the expression \( \sqrt{8} + \sqrt{18} - \sqrt{32} \), we first simplify each square root.
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Simplify \( \sqrt{8} \): \[ \sqrt{8} = \sqrt{4 \cdot 2} = \sqrt{4} \cdot \sqrt{2} = 2\sqrt{2} \]
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Simplify \( \sqrt{18} \): \[ \sqrt{18} = \sqrt{9 \cdot 2} = \sqrt{9} \cdot \sqrt{2} = 3\sqrt{2} \]
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Simplify \( \sqrt{32} \): \[ \sqrt{32} = \sqrt{16 \cdot 2} = \sqrt{16} \cdot \sqrt{2} = 4\sqrt{2} \]
Now, we substitute the simplified values back into the original expression: \[ \sqrt{8} + \sqrt{18} - \sqrt{32} = 2\sqrt{2} + 3\sqrt{2} - 4\sqrt{2} \]
Next, we combine the terms: \[ (2\sqrt{2} + 3\sqrt{2} - 4\sqrt{2}) = (2 + 3 - 4)\sqrt{2} = 1\sqrt{2} = \sqrt{2} \]
Thus, the value of the expression \( \sqrt{8} + \sqrt{18} - \sqrt{32} \) is: \[ \boxed{\sqrt{2}} \]