Evaluate –x^2 + 2x – 4 for x = 5

Question

Can someone review the process for this? Thank you!

 

Answer 1

Hi Abby,

 

For x=5,

 

-x²+2x-4   = -(5)²+2(5)-4

 

                =-25+10-4

 

                =-15-4

 

                =-19

Answer 2

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.

Answer 3

-x² + 2x - 4.......................where x = 5

 

substitute x into the equation.

 

-(5)² + 2(5) - 4

 

= -25 + 10 - 4

 

= -19