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20 votes
20 votes
If f(x) =x^2-x , then evaluate f(a-4)

User AxFab
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2 Answers

16 votes
16 votes

Answer:

Explanation:

'x' shows up 3 times in f(x) =x^2-x. To evaluate f(a - 4), replace each instance of 'x' with 'a - 4:'

f(a - 4) = (a - 4)^2 - (a - 4)

This result could be left as is, or it could be expanded:

f(a - 4) = a^2 - 8a + 16 - a + 4, or

f(a - 4) = a^2 - 9a + 20

User Teej
by
2.3k points
15 votes
15 votes

Answer:


→ \: { \tt{f(x) = {x}^(2) - x }}

• when f(x) is f(a-4), x is (a - 4):


→ \: { \tt{f(a - 4) = {(a - 4)}^(2) - a}}

• Expand the bracket, from quadratic equation rules:


{ \boxed{ \bf{ {(a - b)}^(2) = {a}^(2) - 2ab + {b}^(2) }}}

• therefore:


→ \: { \tt{f(a - 4) = ( {a}^(2) - 8a + 16) - a}} \\ \\ → \: { \boxed{ \tt{f(a - 4) = {a}^(2) - 9a + 16}}}

User Jay Ordway
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2.9k points