For the function f(x) = x^3, determine ((f(a+h) - f(a))/h

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

The function f(x) = x^3.

To determine f(a+h) substitute x with a+h.

f(a+h) = (a+h)^3

= a^3 +3*a^2*h +3*a*h^2+ h^3

f(a) = a^3

`(f(a+h) - f(a))/h`

= `(a^3+3*a^2*h +3*a*h^2+ h^3 - a^3)/h`

= `(3*a^2*h +3*a*h^2+ h^3)/h`

= `3*a^2 +3*a*h+ h^2`

The simplified form of `(f(a+h) - f(a))/h` for `f(x) = x^3` is `3*a^2 +3*a*h+ h^2`

Which equals `3a^2`  since` ` h = 0.

hardik-kalasua's profile pic

hardik-kalasua | In Training Educator

Posted on

Given `f(x)=x^3 ` .

To determine `(f(a+h)-f(a))/h ` :

put x=(a+h) in f(x) to obtain
`f(a+h)=(a+h)^3 = a^3 + h^3 + 3*a^2*h + 3*a*h^2 `

Therefore, `(f(a+h)-f(a))/h = ((a^3 + h^3 + 3*a^2*h + 3*a*h^2) - (a^3))/h`

                                     `= (h^3 + 3*a^2*h + 3*a*h^2)/h`

                                     `= h^2 + 3*a^2 + 3*a*h `

and when `h->0` , `(f(a+h) - f(a))/h -> f'(x) = 3*a^2 `

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