Posted by **Hannah** on Saturday, February 5, 2011 at 11:31am.

Find the derivative of f(x)= 2 sqrt x at x=4.

i thought that the derivative would be 2 x^1/2 but I guess this is wrong.

- Math -
**helper**, Saturday, February 5, 2011 at 1:09pm
dy/dx 2x^(1/2)

2 * 1/2 x^(1/2 - 2/2)

2/2 x^(-1/2) = x^(-1/2) = 1/(sqrt(x))

- Math -
**dave**, Saturday, February 5, 2011 at 1:17pm
You have two problems here.

1. need D:f(x) = 2sqrtx

2. subsitute x=4 into derivative

D: 2sqrtx :

a) multiply power times coefficient; 1/2 * 2 = 1

b)power - 1 = 1/2 -1 = -1/2

c. f'(x) = x^-1/2 or 1/sqrtx

substitute 4 for x and you should be there

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