If #f(x) = 2x^2- x# , what is f(-3)?

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Answer 1 · 2016-08-13T13:48:16

#f(-3)=21#

To evaluate f( -3) substitute x = - 3 into f(x)

#rArrf(color(red)(-3))=2(color(red)(-3))^2-(color(red)(-3))#

#=(2xx9)+3=21#

Answer 2 · 2016-08-13T13:51:13

#f(-3)=21#

For any function #f(x)# to find #f(a)# for a constant number #a#, we have just put #x=a# in #f(x)# and we get #f(a)#.

As #f(x)=2x^2-x#,

#f(-3)=2×(-3)^2-(-3)#

= #2×9+3#

= #18+3=21#