Help with differentiation (1 Viewer)

[dimzi]

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

 

[RideTheLightnin]

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

Id use the product rule
y' = uv' + vu'

 

[speed2]

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]

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]

That is the part I dont get.

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

yeah

10char

 

[Antwan23q]

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]

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]

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.

 

[RideTheLightnin]

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....

 

[pLuvia]

25(1-t/60)²
= 50(1-t/60) x -1/60
= -5/6(1 - t/60)