The Student Room Group
Reply 1
You need the product rule to do this:

d/dx(uv) = (du/dx).v + u.(dv/dx)

So your function becomes

(3x^2)(x-1)^2 = 2x^3(x-1)
Reply 2
eek
this is probably a really simple question seein as though its question one of the chapter!! but im not sure on how to complete it...so please help!.....the question is:

differentiate:
x^3(x-1)^2

thanks!

[d/dx]x^3(x - 1)^2 = 3x^2.(x - 1)^2 + (x^3).2.(x - 1)

Ben

Sorry - saw Fermat's post and realised that I hadn't squared an x.
Reply 3
eek
this is probably a really simple question seein as though its question one of the chapter!! but im not sure on how to complete it...so please help!.....the question is:

differentiate:
x^3(x-1)^2

thanks!


y = x³(x-1)²
y' = 3x²(x-1)² + 2x³(x-1)
eek
differentiate:
x^3(x-1)^2


Let u = x^3 ---> du/dx = 3x^2

Let v = (x-1)^2 ---> dv/dx = 2(x-1)

Hence: d/dx [x^3(x-1)^2] = u(dv/dx) + v(du/dx) = x^3[2(x-1)] + (x-1)^2[3x^2]

= x^3[2x-2] + 3x^2(x-1)(x-1)

= 2x^4 - 2x^3 + 3x^2(x^2 - 2x + 1)

= 2x^4 - 2x^3 + 3x^4 - 6x^3 + 3x^2

= 5x^4 - 8x^3 + 3x^2

---> d/dx [x^3(x-1)^2] = 5x^4 - 8x^3 + 3x^2
Reply 5
Invisible
Let u = x^3 ---> du/dx = 3x^2

Let v = (x-1)^2 ---> dv/dx = 2(x-1)

Hence: d/dx [x^3(x-1)^2] = u(dv/dx) + v(du/dx) = x^3[2(x-1)] + (x-1)^2[3x^2]

= x^3[2x-2] + 3x^2(x-1)(x-1)

= 2x^4 - 2x^3 + 3x^2(x^2 - 2x + 1)

= 2x^4 - 2x^3 + 3x^4 - 6x^3 + 3x^2

= 5x^4 - 8x^3 + 3x^2

---> d/dx [x^3(x-1)^2] = 5x^4 - 8x^3 + 3x^2


If you're going to expand it out, you might as well do that first and not use the product rule.

Ben
Reply 6
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eek
OP
got it!.....thank you all!
Reply 7
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eek
OP
ok...i got that but now.....i dont get the example in the book: it goes....

Given that y=3x^3 (2x-5)^4 find dy/dx

dy/dx = v(du/dx) + u(dv/dx)

=9x^2(2x-5)^4 + 3x^3 . 8(2x-5)^3

i get that bit but then it jumps to the next step and ive dont know what they've done to get their..the next step is

= 3x^2(2x-5)^3[3(2x-5)+8x] <----how did they get this??!
Reply 8
eek
ok...i got that but now.....i dont get the example in the book: it goes....

Given that y=3x^3 (2x-5)^4 find dy/dx

dy/dx = v(du/dx) + u(dv/dx)

=9x^2(2x-5)^4 + 3x^3 . 8(2x-5)^3

i get that bit but then it jumps to the next step and ive dont know what they've done to get their..the next step is

= 3x^2(2x-5)^3[3(2x-5)+8x] <----how did they get this??!


They just took to the 3x^2(2x-5)^3 out, as it is a common factor to all parts of the equation.
Reply 9
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eek
OP
ohh! k...thanx!

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