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If f(x)=x^2-3 and g(x)=5x-2, evaluate f(-1)-g(2)?

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rosey-girl | Student, Grade 12 | (Level 1) Valedictorian

Posted May 2, 2013 at 12:59 AM via web

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If f(x)=x^2-3 and g(x)=5x-2, evaluate f(-1)-g(2)?

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oldnick | (Level 1) Valedictorian

Posted May 2, 2013 at 1:07 AM (Answer #1)

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`f(x)=x^2-3`    `g(x)=5x-2`

`f(-1)=(-1)^2-3=1-3=-2`   `g(2)=5 xx 2-2=10-2=8`

So  `f(-1) - g(2)= -2-8=-10`

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lfryerda | High School Teacher | (Level 2) Educator

Posted May 2, 2013 at 1:08 AM (Answer #2)

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To evaluate expressions like `f(-1)-g(2)` , we need to remember that a function evaluation is just a number, and that two numbers may be subtracted like in that expression.  This means that each function needs to be evaluated separately, then subtracted.

`f(-1)-g(2)`   sub -1 in f(x) and 2 in g(x)

`=((-1)^2-3)-(5(2)-2)`   now evaluate, being careful with order of operations

`=(1-3)-(10-2)`   continue to work from the inside out

`=(-2)-8`

`=-10`

The expression evaluates to -10.

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