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Help with differentiation (1 Viewer)

dimzi

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Ok I have to differentiate this:

25(1 - t/60)^2

I got 50(1 - t/60). t/3600 ..... but the last part is not right :S and the answers find the derivative of the brackets as 1/60. How do they get this? Where does the t go?

Please help :)
 

speed2

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u use the chain rule

consider y=25(1 - t/60)2
let u = 1 - t/60
then y=25u2

you're trying to find dy/dt right?
dy/dt=(dy/du).(du/dt)

now y=25u2
so dy/du=50u
or = 50(1-t/60) as u = 1 - t/60

and u = 1 - t/60
so du/dt = -1/60 (this is because t/60 is same as (1/60) x t)

therefore dy/dt = -(50/60)x(1 - t/60)
 

dimzi

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speed2 said:
and u = 1 - t/60
so du/dt = -1/60 (this is because t/60 is same as (1/60) x t)
That is the part I dont get.

Is it the same principle as that of the derivative of x is 1?

I understand everything else, its just that the differentiation of fractions shit me.

I tried bringing the 60 up with the numerator and a negative power, but then thats how I ended up with t/3600.
 

speed2

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dimzi said:
That is the part I dont get.

Is it the same principle as that of the derivative of x is 1?
yeah

10char
 

Antwan23q

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y=25(1-t/60)^2
y'=50(1-t/60)(-1/60)
y'=(-5/6)(1-t/60)

you dont do the derivative of a fraction
in this example,
-t/60 is another way of saying (-1/60)t
and (-1/60) is a constant.
so the derivative of (-1/60)t
is just (-1/60)
 

dimzi

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antwan2bu said:
y=25(1-t/60)^2
y'=50(1-t/60)(-1/60)
y'=(-5/6)(1-t/60)

you dont do the derivative of a fraction
in this example,
-t/60 is another way of saying (-1/60)t
and (-1/60) is a constant.
so the derivative of (-1/60)t
is just (-1/60)
Ohhhh that makes it much clearer!!

Have got it now, thanks heaps speed2 and antwan2bu!! :)
 

rnitya_25

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RideTheLightnin said:
Hmm im not sure...have you got the answer there?

Id use the product rule
y' = uv' + vu'
you would not use the product rule because its not a function in a function. 25 is not a function, its just a constant. therefore the derivative is basically what antwanbu and speed said.
 
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rnitya_25 said:
you would not use the product rule because its not a function in a function. 25 is not a function, its just a constant. therefore the derivative is basically what antwanbu and speed said.
lol yeah.....

i should of studied in yr 11....
 

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