Saturday, July 21, 2012

If f(x) = x^sqrt(x^2+3)+10 , find the value of f'(1).

You can only ask one question at a time. I am providing
the value of f'(1).


We have to find the derivative of f(x)
= x^sqrt(x^2+3)+10


Let g(x) =
x^sqrt(x^2+3)


ln (g(x)) = sqrt( x^2 + 3) ln
x


1/(g(x)) * g'(x) = [sqrt( x^2 + 3)]'*ln x + sqrt( x^2 +
3)*[ln x]'


1/(g(x))*g'(x) = (1/2)*2x*(1/sqrt( x^2 + 3))*ln
x + sqrt(x^2 + 3)*(1/x)


g'(x) = [(1/2)*2x*(1/sqrt( x^2 +
3))*ln x + sqrt(x^2 + 3)*(1/x)](x^sqrt(x^2+3))


=>
g'(x) = [x^2*ln x +(x^2 + 3)](x^sqrt(x^2+3))/x*(sqrt( x^2 +
3))


=> g'(x) = [(x^sqrt(x^2+3))*x^2*ln x
+(x^sqrt(x^2+3))(x^2 + 3)](x^sqrt(x^2+3))/x*(sqrt( x^2 +
3))


=> g'(x) = [(x^sqrt(x^2+3)+2)*ln x
+(x^sqrt(x^2+3))(x^2 + 3)]/x*(sqrt( x^2 + 3))


We see that
f'(x) = g'(x)  as 10 is a constant.


f'(x) =
[(x^sqrt(x^2+3)+2)*ln x +(x^sqrt(x^2+3))(x^2 + 3)]/x*(sqrt( x^2 +
3))


f'(1) = 1*4/2


=>
f'(1) = 2


The required value of f'(1) =
2.

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