# Math Help - find derivative without using product//chain/or quotient rule..

1. ## find derivative without using product//chain/or quotient rule..

Hello,

Please could someone run through deriving these 2 equations through algebraic expansion.

d/dx {sqrt(2y)}

and

d/dx {-1/((2x)^3)}

2. ## Re: find derivative without using product//chain/or quotient rule..

edit ... just figured out the second one..
the first one I still can't get my head around!

i'll run through what i'm doing ..

so,

d/dx[2y]^1/2

= 1/2*[2y]^-1/2

= 1/2*(1/sqrt(2y)

=1/(2*sqrt(2y)) ....

i should be getting 1/sqrt(2y) ... where am i going wrong?

3. ## Re: find derivative without using product//chain/or quotient rule..

Sqrt(2x)= sqrt(2)*sqrt(x)

4. ## Re: find derivative without using product//chain/or quotient rule..

Hello, euphmorning!

the first one . . .

So: . $\frac{d}{dx}\left[(2x)^{\frac{1}{2}}\right]$

. . . . $=\;\tfrac{1}{2}\cdot(2x)^{-\frac{1}{2}}{\color{red}\cdot 2}$

5. ## Re: find derivative without using product//chain/or quotient rule..

Heya, thanks for the responses.. i'm afraid I still can't see how to arrive @ 1/sqrt(2y)

:/

6. ## Re: find derivative without using product//chain/or quotient rule..

The sqrt(2) is a constant so take the derivative of sqrt(x). 1/2(sqrt(x)). Multiply by the constant and arrive at sqrt(2)/2(sqrt(x)). Multiply that by sqrt(2)/sqrt(2) to get your answer.

7. ## Re: find derivative without using product//chain/or quotient rule..

Got it at last, thankyou very much.