To complete the square for the polynomial \( w^2 + 28w \), we follow these steps:
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Start with the polynomial: \[ w^2 + 28w \]
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Take the coefficient of \( w \), which is \( 28 \), and divide it by \( 2 \): \[ \frac{28}{2} = 14 \]
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Square this result: \[ 14^2 = 196 \]
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The polynomial \( w^2 + 28w \) can be rewritten as: \[ w^2 + 28w + 196 - 196 = (w + 14)^2 - 196 \]
Thus, the number that makes the polynomial a perfect-square quadratic is: \[ \boxed{196} \]
Now the final expression can be written as \( (w + 14)^2 \).