Final answer:
To make the expression a perfect-square trinomial, the missing value is 25.
Step-by-step explanation:
In order for a polynomial to be a perfect-square trinomial, the last term must be the square of half of the coefficient of the second term. In this case, the coefficient of the second term is -10, so half of that is -5. Therefore, the missing value to make the expression a perfect-square trinomial is 25.
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