TheAlphaParticle
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Name:  Screenshot 2016-10-25 at 20.21.05.png
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Size:  23.2 KB SO i need help on the part (iii)
So far i've got  f(x-1)= \frac{{e^{2x-1}} \times {e^{2x}}} {{x^2}\times{x-1}^2}}}
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aoxa
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(Original post by TheAlphaParticle)
Name:  Screenshot 2016-10-25 at 20.21.05.png
Views: 118
Size:  23.2 KB SO i need help on the part (iii)
So far i've got  f(x-1)= \frac{{e^{2x-1}} \times {e^{2x}}} {{x^2}\times{x-1}^2}}}
I have no idea how you managed to get that for f(x-1). To get f(x-1) you should have subbed (x-1) into wherever you saw an (x) in the original f(x).
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agrajaag
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It should be f(x-1) = \frac{e^{2(x-1)}}{(x-1)^2}
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jamestg
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Is it k=e^-2 ?
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NotNotBatman
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(Original post by jamestg)
Is it k=e^-2 ?
Yes.
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jamestg
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(Original post by NotNotBatman)
Yes.
Cracking. Well, that's my c3 revision done for today.
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Naruke
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(Original post by jamestg)
Is it k=e^-2 ?
Questions like these never come up in Edexcel, they always ask some basic stuff like differentiate sin x

think I may do mei papers from now on
Spoiler:
Show

f(x-1) = \frac{e^2^(^x^-^1^)}{(x-1)^2}

 \frac{e^2^(^x^-^1^)}{(x-1)^2}  = k(\frac{x}{x-1})^2 \times \frac{e^2^x}{x^2}

\frac{e^2^(^x^-^1^)}{(x-1)^2} = k \times \frac{x^2e^2^x}{(x-1)^2x^2}

 \frac{\frac{e^2^(^x^-^1^)}{(x-1)^2}}{\frac{x^2e^2^x}{(x-1)^2x^2}} = k

 k = \frac{e^2^(^x^-^1^)}{(x-1)^2}  \times \frac{(x-1)^2x^2}{x^2e^2^x}

k= \frac{e^2^(^x^-^1)}{e^2^x}

k= e^2^(^x^-^1^)^-^(^2^x^)

k = e^-^2
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jamestg
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(Original post by Naruke)
Questions like these never come up in Edexcel, they always ask some basic stuff like differentiate sin x

think I may do mei papers from now on
Spoiler:
Show

f(x-1) = \frac{e^2^(^x^-^1^)}{(x-1)^2}

 \frac{e^2^(^x^-^1^)}{(x-1)^2}  = k(\frac{x}{x-1})^2 \times \frac{e^2^x}{x^2}

\frac{e^2^(^x^-^1^)}{(x-1)^2} = k \times \frac{x^2e^2^x}{(x-1)^2x^2}

 \frac{\frac{e^2^(^x^-^1^)}{(x-1)^2}}{\frac{x^2e^2^x}{(x-1)^2x^2}} = k

 k = \frac{e^2^(^x^-^1^)}{(x-1)^2}  \times \frac{(x-1)^2x^2}{x^2e^2^x}

k= \frac{e^2^(^x^-^1)}{e^2^x}

k= e^2^(^x^-^1^)^-^(^2^x^)

k = e^-^2
Is MEI harder/more involved than edexcel? I'm currently on one past paper per week but I want to do more!
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Naruke
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(Original post by jamestg)
Is MEI harder/more involved than edexcel? I'm currently on one past paper per week but I want to do more!
Well, there is a reason why Edexcel is the most widely taken exam board for maths
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jamestg
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(Original post by Naruke)
Well, there is a reason why Edexcel is the most widely taken exam board for maths
That can't be the reason! It's probably down to resources

But I'll give a few papers a go
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RDKGames
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#11
(Original post by Naruke)
Questions like these never come up in Edexcel, they always ask some basic stuff like differentiate sin x

think I may do mei papers from now on
Spoiler:
Show

f(x-1) = \frac{e^2^(^x^-^1^)}{(x-1)^2}

 \frac{e^2^(^x^-^1^)}{(x-1)^2}  = k(\frac{x}{x-1})^2 \times \frac{e^2^x}{x^2}

\frac{e^2^(^x^-^1^)}{(x-1)^2} = k \times \frac{x^2e^2^x}{(x-1)^2x^2}

 \frac{\frac{e^2^(^x^-^1^)}{(x-1)^2}}{\frac{x^2e^2^x}{(x-1)^2x^2}} = k

 k = \frac{e^2^(^x^-^1^)}{(x-1)^2}  \times \frac{(x-1)^2x^2}{x^2e^2^x}

k= \frac{e^2^(^x^-^1)}{e^2^x}

k= e^2^(^x^-^1^)^-^(^2^x^)

k = e^-^2
If those exam question's aren't feeling challenging, you can have a go at deriving the general result for the nth derivative of a product of two functions, fg. And who knows, perhaps this result can help you with whatever else.
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Naruke
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(Original post by RDKGames)
If those exam question's aren't feeling challenging, you can have a go at deriving the general result for the nth derivative of a product of two functions, fg. And who knows, perhaps this result can help you with whatever else.

let  y = fg

 y' = f'g + fg'

 y'' = f''g+2f'g' + fg''

 y''' = f'''g +3f''g' + 3f'g'' + fg'''
.
.
.
 y^n = \displaystyle\sum_{r=0}^{n} \frac{n!}{r!(n-r)!} f^ng^n^-^r
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RDKGames
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#13
(Original post by Naruke)
let  y = fg

 y' = f'g + fg'

 y'' = f''g+2f'g' + fg''

 y''' = f'''g +3f''g' + 3f'g'' + fg'''
.
.
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 y^n = f^ng + n(f^n^-^1g^n^-^2+f^n^-^2g^n^-^1)+fg^n
Does that hold for n=4?
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Naruke
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(Original post by RDKGames)
Does that hold for n=4?
nope oh i see now

pascal
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