Question

Expand and simplify I (X -5)(X +4)

Answer 1

The answer you are looking for is:
Expand (X-5)(X-4):
X^(2)+4x-5x-20 :
Then add like terms to simplify: 
X^(2)-X-20 
Hope that helps!! 
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Answer 2

To expand, use distributive property:
(x - 5)(x + 4)
x^2 + 4x - 5x - 20
Simplify by adding like terms:
x^2 - x - 20