Question

f(x)= x^2 / (x-2)    find f'(1)

Accepted Answer

f(x) = x^2 /(x-2)
We know that if f= u/v , then f'= (u'v-uv')/v^2
Now we will assume that:
u= x^2 ==> u'=2x
v= x-2 ==> v' =1
Then f'(x) = [2x(x-2)- x^2(1)]/(x-2)^2
              = (2x^2 -4x -x^2 )/(x-2)^2
               = (x^2 -4x)/(x-2)^2
Now we will substitute with x=1
f'(1) = (1-4)/(1-2)^2
       = -3/ 1= -3
Then f'(1)= -3

Answer

The function f(x)= x^2 / (x-2) .
Use the property x^-1 = 1/x . This allows us to write the given function f(x)= x^2 / (x-2)   as f(x)= x^2*(x-2)^-1 .
If y = f(x)*g(x) , y' = f'(x)*g(x) + f(x)*g'(x) and if y = x^n, y' = n*x^(n-1) 
For the given function f(x)= x^2*(x-2)^-1 
f'(x) = (x^2)'*(x - 2)^-1 + x^2*((x-2)^-1)'
= 2x*(x - 2)^-1 + x^2*-1*(x - 2)^-2
At x = 1, 2x*(x - 2)^-1 + x^2*-1*(x - 2)^-2 = 2*1*(1 - 2)^-1 + 1^2*-1*(1 - 2)^-2
= 2*-1 + -1*(1/1)
= -2 - 1
= -3
The derivative of f(x)= x^2 / (x-2) at x = 1 is -3

Answer

f(x)=x^2/(x-2)
D= R-{2} ;than we could write
f(x)'= (x^2)'(x-2)-[(x-2)'(x^2)]/(x-2)^2
f(x)'= 2x(x-2)-1(x^2)/(x-2)^2
f(x)'=2x^2-4x-x^2/(x-2)^2
f(x)'=x^2-4x/(x-2)^2
f(x)'=x(x-4)/(x-2)^2
finally f(1)'=1(1-4)/1-2)^2

Answer

Another method to calculate a derivative of a function in a point is:
f'(1) = limit [f(x)-f(1)]/(x-1) = lim [x^2/(x-2) + 1]/(x-1)
f'(1) = lim (x^2 + x - 2)/(x-2)(x-1) = 0/0
If we'll substitute x by 1 into the numerator expression, we'll cancel it, so x=1 is the root of both, numerator and denominator. We'll write the numerator as a product.
x^2 + x - 2 = (x-1)(x+2)
f'(1) = lim (x-1)(x+2)/(x-1)(x-2) = lim (x+2)/(x-2)
f'(1) = (1+2)/(1-2) = 3/-1 = -3

Answer

f(x) = x^2/(x-2). To find f'(10.
Solution:
We first find f'(x) and then find the value of f'(x) at x=1.
f(x) = x^2/(x-2)
=  (x^2-2x)+2x/(x-2)
= (x(x-2) + 2(x-2)+4)/(x-2)
=x +2 +4/(x-2)
f'(x) = {x +2  +4(x-2)}'.
= (x)'+(2)' +(4/(x-2))'. Using (d/dx)x^n  = nx^(n-1) ..
= 1 +0  -2/(x-2)^2 , as (d/dx) (ax+b)^n = n(ax+b)^(n-1)* a. Therefore,
f'(x) = 1 -2/(x-2)^2.
f'(1) = 1  -2/(1-2)^2 =  1  -2/1 =  -1

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f(x)= x^2 / (x-2) find f'(1)

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