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find the value of dy/dx when x=1  (a are constant)

i)y=(√x-3)(√x-4)  *only the x are under the square root

ii)y=a/x - x/a

iii)y=3(4x^-1 - 2x^-2)

 Oct 26, 2015

Best Answer 

 #2
avatar+130515 
+5

Here's another way to do the first one

 

y = (x1/2  - 3 ) (x1/2 - 4)   =  ( x - 7x1/2 + 12)

 

And differentiating term by term  we have

 

1 - (7/2)x-1/2

 

So

 

y ' (1)   =  1 - 7/2   =  -5/2

 

 

cool cool cool

 Oct 26, 2015
 #1
avatar+118723 
+5

find the value of dy/dx when x=1  (a are constant)

i)y=(√x-3)(√x-4)  *only the x are under the square root

 

\(y=(\sqrt{x}-3)(\sqrt{x}-4)\\ \qquad let\\ \qquad u=x^{0.5}-3 \qquad v=x^{0.5}-4\\ \qquad u'=0.5x^{-0.5} \qquad v=0.5x^{-0.5}\\ y'=uv'+vu' \\ \mbox{Can you finish it?}\)

 

 

 

 

ii)y=a/x - x/a

\(y=ax^{-1}-\frac{x}{a}\\ y'=-1ax^{-2}-\frac{1}{a}\\ y'(1)=-1-\frac{1}{a}\)

 

 

 

iii)y=3(4x^-1 - 2x^-2)

 

\(y=3(4x^{-1}-2x^{-2})\\ y'=3(-4x^{-2}+4x^{-3})\\ y'(1)=3(-4+4)=0\)

 Oct 26, 2015
 #2
avatar+130515 
+5
Best Answer

Here's another way to do the first one

 

y = (x1/2  - 3 ) (x1/2 - 4)   =  ( x - 7x1/2 + 12)

 

And differentiating term by term  we have

 

1 - (7/2)x-1/2

 

So

 

y ' (1)   =  1 - 7/2   =  -5/2

 

 

cool cool cool

CPhill Oct 26, 2015

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