Answer:
f ( x ) = ( x - 5 ) ² - 20
Step-by-step explanation:
1- Add the same value to both sides
f ( x ) = x ² - 10x + 5
2- Add 25 to the expression
f ( x ) + ? = x ² - 10x + ? + 5
3- Add 25 to the left-hand side
f ( x ) + ? = x ² - 10x + 25 + 5
4- Factor the expression
f ( x ) + 25 = x ² - 10x + 25 + 5
5- Move the constant to the right
f ( x ) + 25 = ( x - 5 ) ² + 5
6- Calculate
f ( x ) = ( x - 5) ² + 5 - 25
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