f(x)x^3
f(5)= 5^3=125
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2)f(x)=x^2-4/x-2
f(5) = (5^2 - 4) / (5-2) = 21 \ 3 = 7
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3) f(x)=3x^2-5x+1
f(5) = 3*5^3 - 5*5 +1 = 3*125 - 25 +1 = 375 - 24= 351
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