Limit

Calculus Level 2

0 1/8 1 Infinity

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2 solutions

Brock Brown
Sep 29, 2015

When we try to plug in 1, we end up with the indeterminate form 0 0 \frac{0}{0} :

3 + 5 3 2 1 2 1 = 0 0 \frac{\sqrt[3]{3+5} - 2}{1^2-1} = \frac{0}{0}

This means we can try to evaluate the limit using L'Hopital's rule by replacing the numerator and the denominator with their derivatives. The derivative of 3 x + 5 3 2 \sqrt[3]{3x+5} - 2 can be calculated more easily if we translate it to its power form ( 3 x + 5 ) 1 3 2 (3x+5)^{\frac{1}{3}} - 2 . We can apply the chain and power rules here and say that the derivative of the numerator is 1 3 ( 3 x + 5 ) 2 3 × 3 = ( 3 x + 5 ) 2 3 \frac{1}{3}(3x+5)^{-\frac{2}{3}} \times 3 = (3x+5)^{-\frac{2}{3}} . Power rule says that the derivative of the denominator is 2 x 2x .

So we're left with:

lim x 1 ( 3 x + 5 ) 2 3 2 x = 1 4 2 = 1 8 \lim_{x \to 1} \frac{(3x+5)^{-\frac{2}{3}}}{2x} = \frac{\frac{1}{4}}{2} = \boxed{\frac{1}{8}}

ARE YOU GOOD AT EVERYTHING? YOU ROCK!!!!

Pi Han Goh - 5 years, 8 months ago

Algebric solution:

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