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I multiplied out the top to give x^2 - 5x - 24 over x.

Now I'm confused because I differentiated it to give :
2x-5 over 1 , but the answer involves subtracting the top from bottom :confused: . Why does subtracting happen before the differentiation ?
(edited 13 years ago)
You can cancel this down further to x - 5 - 24/x, which is a much easier way to differentiate.

This seems to be an AS question, it's not as simple when you have a quotient just to differentiate top and then bottom (explained at A2).
Reply 2
Avatar for Femto
Femto
8
Original post by WildBerry


------

I multiplied out the top to give x^2 - 5x - 24 over x.

Now I'm confused because I differentiated it to give :
2x-5 over 1 , but the answer involves subtracting the top from bottom :confused: . Why does subtracting happen before the differentiation ?


Is this an AS question?
Reply 3
Avatar for WildBerry
WildBerry
OP
Yeah C1 question AS
Reply 4
Avatar for ilyking
ilyking
Original post by WildBerry


------

I multiplied out the top to give x^2 - 5x - 24 over x.

Now I'm confused because I differentiated it to give :
2x-5 over 1 , but the answer involves subtracting the top from bottom :confused: . Why does subtracting happen before the differentiation ?


y=(x+3)(x−8)x=x2−5x−24x=x2x−5xx−24x=x−5−24x y = \frac{(x+3)(x-8)}{x}= \frac{x^2-5x-24}{x}= \frac{x^2}{x}- \frac{5x}{x} - \frac{24}{x} = x - 5 - \frac {24}{x}

then

dydx=1+24x2 \frac{dy}{dx} = 1 + \frac{24}{x^2}

now do you understand?
(edited 13 years ago)
Reply 5
Avatar for WildBerry
WildBerry
OP
Original post by ilyking
y=(x+3)(x−8)x=x2−5x−24x=x2x−5xx−24x=x−5−24x y = \frac{(x+3)(x-8)}{x}= \frac{x^2-5x-24}{x}= \frac{x^2}{x}- \frac{5x}{x} - \frac{24}{x} = x - 5 - \frac {24}{x}

then

dydx=1+24x2 \frac{dy}{dx} = 1 + \frac{24}{x^2}

now do you understand?


Thanks alot , that made it seem much easier =)

Yeah , y= is when its all subtracted out , dy/dx is that differntiated
(edited 13 years ago)
Reply 6
Avatar for ilyking
ilyking
Original post by WildBerry
Thanks alot , that made it seem much easier =)

Yeah , y= is when its all subtracted out , dy/dx is that differntiated


subtracted isn't the right word. "Simplified" is.

Just make sure you know when you start the differentiation process (simplify first completely, then begin the differentiated).

Glad to help you :five:

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