Answer:
y value = 49
Explanation:
You are going to be completing the square
y = - x^2 - 10x + 24 Take a minus outside the brackets for the first 2 terms.
y = - (x^2 + 10x) + 24
Take 1/2 the linear term (1/2 10 and square it. Put that value inside the brackets. 1/2* 10 =5; 5^2 = 25
y = - (x^2 + 10x + 25) + 24
Add 25 outside the brackets.
y = -(x^2 + 10x + 25) + 24 + 25. You should stop here and consider why you are adding 25 outside the brackets. It is because there is a - sign in front of the trinomial and what is inside the brackets is really - 25 when the brackets are removed. Therefore to balance that, you add 25.
Now complete the square.
y = - ( x + 5)^2 + 49
The value you seek is 49.
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I'll confirm this with a graph.