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Find 
lim_(x rarr1)(x-1)/(sqrt(5x-1)-2).
Choose 1 answer:
(A) 
(5)/(2)
(B) 
(4)/(5)
(C) 
-(1)/(5)
(D) The limit doesn't exist

Find limx1x15x12 \lim _{x \rightarrow 1} \frac{x-1}{\sqrt{5 x-1}-2} .\newlineChoose 11 answer:\newline(A) 52 \frac{5}{2} \newline(B) 45 \frac{4}{5} \newline(C) 15 -\frac{1}{5} \newline(D) The limit doesn't exist

Full solution

Q. Find limx1x15x12 \lim _{x \rightarrow 1} \frac{x-1}{\sqrt{5 x-1}-2} .\newlineChoose 11 answer:\newline(A) 52 \frac{5}{2} \newline(B) 45 \frac{4}{5} \newline(C) 15 -\frac{1}{5} \newline(D) The limit doesn't exist
  1. Substitute x=1x = 1: To find the limit of the given function as xx approaches 11, we first substitute x=1x = 1 into the function to see if it results in an indeterminate form.\newlinelimx1x15x12=115112=0512=022=00\lim_{x \to 1}\frac{x-1}{\sqrt{5x-1}-2} = \frac{1-1}{\sqrt{5\cdot1-1}-2} = \frac{0}{\sqrt{5-1}-2} = \frac{0}{2-2} = \frac{0}{0}\newlineSince we get 0/00/0, which is an indeterminate form, we need to use algebraic manipulation to simplify the expression and resolve the indeterminate form.
  2. Multiply by conjugate: To eliminate the square root in the denominator, we can multiply the numerator and the denominator by the conjugate of the denominator. The conjugate of 5x12\sqrt{5x-1}-2 is 5x1+2\sqrt{5x-1}+2.limx1x15x125x1+25x1+2=(x1)(5x1+2)(5x12)(5x1+2)\lim_{x \to 1}\frac{x-1}{\sqrt{5x-1}-2} \cdot \frac{\sqrt{5x-1}+2}{\sqrt{5x-1}+2} = \frac{(x-1)(\sqrt{5x-1}+2)}{(\sqrt{5x-1}-2)(\sqrt{5x-1}+2)}
  3. Simplify denominator: Now we simplify the denominator using the difference of squares formula: (ab)(a+b)=a2b2(a-b)(a+b) = a^2 - b^2. The denominator becomes (5x1)2(2)2=(5x1)4=5x5(\sqrt{5x-1})^2 - (2)^2 = (5x-1) - 4 = 5x - 5.
  4. Expand numerator: The numerator is expanded by distributing x1x-1 to both terms in the conjugate 5x1+2\sqrt{5x-1}+2. The numerator becomes x(5x1)+2x5x12x(\sqrt{5x-1}) + 2x - \sqrt{5x-1} - 2.
  5. Factor out common terms: Now we have the following limit: limx1[x(5x1)+2x5x12]/(5x5)\lim_{x \to 1}\left[ x(\sqrt{5x-1}) + 2x - \sqrt{5x-1} - 2 \right]/(5x - 5) We can simplify this by factoring out common terms and canceling them out.
  6. Cancel out common factor: We notice that the numerator and denominator both have terms that can be factored by x1x-1. The numerator can be rewritten as (x1)(5x1+2)(x-1)(\sqrt{5x-1}+2) and the denominator as 5(x1)5(x-1). Now we have: limx1(x1)(5x1+2)5(x1)\lim_{x \to 1}\frac{(x-1)(\sqrt{5x-1}+2)}{5(x-1)}
  7. Simplify expression: Since (x1)(x-1) is a common factor in both the numerator and the denominator, we can cancel it out, leaving us with: limx1(5x1+2)/5\lim_{x \to 1}\left(\sqrt{5x-1}+2\right)/5
  8. Substitute x=1x = 1: Now we can substitute x=1x = 1 into the simplified expression without getting an indeterminate form: limx1(5x1+25)=(511+25)=(51+25)=(4+25)=(2+25)=45\lim_{x \to 1}\left(\frac{\sqrt{5x-1}+2}{5}\right) = \left(\frac{\sqrt{5\cdot 1-1}+2}{5}\right) = \left(\frac{\sqrt{5-1}+2}{5}\right) = \left(\frac{\sqrt{4}+2}{5}\right) = \left(\frac{2+2}{5}\right) = \frac{4}{5}
  9. Final result: The limit as xx approaches 11 of the given function is 45\frac{4}{5}, which corresponds to answer choice (B).

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