SOLUTION: lim x tends to zero, ((tanx)/x)^(1/x^2) Please send step by stem solution, Regards, S B Roy

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Question 890059: lim x tends to zero, ((tanx)/x)^(1/x^2)
Please send step by stem solution,
Regards,
S B Roy

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
(1)  

We will first find the limit of the natural log of the expression
and then the above will be e raised to the power of the result.

(2)  %22%22=%22%22%22%22=%22%22

lim%5B%22x-%3E0%22%5D++%28+++ln%28tan%28x%29%2Fx%29+%2Fx%5E2%29++%22%22=%22%22

Since (A)  lim%5B%22x-%3E0%22%5D%28tan%28x%29%2Fx%29=1 and ln%281%29=0, and
      (B)  lim%5B%22x-%3E0%22%5D%28x%5E2%29=0

we can use L'Hopital's rule since it has the form 0%2F0.

We need to take the derivative of the numerator and the denominator:

Derivative of numerator:

     matrix%281%2C2%2Cd%2F%28dx%29%2C%28ln%28tan%28x%29%2Fx%29%29%29%22%22=%22%22%22%22=%22%22sec%5E2x%2Ftan%28x%29-1%2Fx%22%22=%22%22
     %281%2Btan%5E2%28x%29%29%2Ftan%28x%29-1%2Fx%22%22=%22%221%2Ftan%28x%29%2Btan%5E2%28x%29%2Ftan%28x%29-1%2Fx%22%22=%22%22cot%28x%29%2Btan%28x%29-1%2Fx%22%22=%22%22
     cos%28x%29%2Fsin%28x%29%2Bsin%28x%29%2Fcos%28x%29-1%2Fx%22%22=%22%22%22%22=%22%22
     %22%22=%22%22%28x%281%29-sin%28x%29cos%28x%29+%29%2F%28x%2Asin%28x%29cos%28x%29%29%22%22=%22%22
     %28x-sin%28x%29cos%28x%29+%29%2F%28x%2Asin%28x%29cos%28x%29%29%22%22=%22%22

     (multiply by 2%2F2 to make use of identity sin(2x)=2sin(x)cos(x):
     %282x-2sin%28x%29cos%28x%29+%29%2F%28x%2A2sin%28x%29cos%28x%29%29%22%22=%22%22%282x-sin%282x%29+%29%2F%28x%2Asin%282x%29%29

Derivative of denominator:  matrix%281%2C2%2Cd%2F%28dx%29%2C%28x%5E2%29%29%22%22=%22%222x

So (2) becomes:

%22%22=%22%22lim%5B%22x-%3E0%22%5D%28%28++2x-sin%282x%29+%29%2F%282x%5E2%2Asin%282x%29+++++%29+%29+%29%22%22=%22%22

Use L'Hopital's rule again:

lim%5B%22x-%3E0%22%5D%28%282-2cos%282x%29%29%2F%284x%5E2cos%282x%29%2B4x%2Asin%282x%29%29%29 (divide top and bottom by 2)


 

Use L'Hopital's rule again:





Divide top and bottom by 2



Use L'Hopital's rule once more:

%22%22=%22%22

No don't need to bother simplifying that, because we can just substitute
x=0

2%2F%28-0-0-0%2B4%2B2%29%22%22=%22%222%2F6%22%22=%22%221%2F3

Therefore the log of the answer is 1%2F3, which means:

%22%22=%22%22




Edwin