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Evaluate –x^2 + 2x – 4 for x = 5

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3 Answers

Hi Abby,
 
For x=5,
 
-x²+2x-4   = -(5)²+2(5)-4
 
                =-25+10-4
 
                =-15-4
 
                =-19
The evaluation of this expression is in the proper reading of the notation:
 
–x^2 + 2x – 4
 
is the same as:
 
= –(x)^2 + 2(x) – 4
 
the parentheses are implicit, but inform the evaluator. This is then rewritten more clearly as:
 
= –(x * x) + 2(x) – 4
 
which then evaluates under x = 5 by:
 
= –(5 * 5) + 2 * 5 – 4
 
where " * " is multiplication. The rest is computation is straightforward, with proper use of order of operations.