Math Problem Statement

Evaluate the limit: lim(x→9) ((√(7x - 62) - 1) / (x - 9))

Solution

The given limit problem is:

limx97x621x9\lim_{{x \to 9}} \frac{\sqrt{7x - 62} - 1}{x - 9}

Approach:

This is an indeterminate form of type 00\frac{0}{0} when you directly substitute x=9x = 9. To resolve this, we can use rationalization by multiplying both the numerator and the denominator by the conjugate of the numerator.

Step-by-step solution:

  1. Multiply by the conjugate: Multiply both the numerator and the denominator by the conjugate of the numerator, 7x62+1\sqrt{7x - 62} + 1:

    7x621x97x62+17x62+1=(7x62)212(x9)(7x62+1)\frac{\sqrt{7x - 62} - 1}{x - 9} \cdot \frac{\sqrt{7x - 62} + 1}{\sqrt{7x - 62} + 1} = \frac{(\sqrt{7x - 62})^2 - 1^2}{(x - 9)(\sqrt{7x - 62} + 1)}

  2. Simplify the numerator: Use the difference of squares in the numerator:

    (7x62)212=(7x62)1=7x63(\sqrt{7x - 62})^2 - 1^2 = (7x - 62) - 1 = 7x - 63

    So the expression becomes:

    7x63(x9)(7x62+1)\frac{7x - 63}{(x - 9)(\sqrt{7x - 62} + 1)}

  3. Factor the numerator: Factor out 77 from the numerator:

    7(x9)7(x - 9)

    Now the expression is:

    7(x9)(x9)(7x62+1)\frac{7(x - 9)}{(x - 9)(\sqrt{7x - 62} + 1)}

  4. Cancel out (x9)(x - 9):

    Since x9x \neq 9, we can cancel (x9)(x - 9) from both the numerator and the denominator:

    77x62+1\frac{7}{\sqrt{7x - 62} + 1}

  5. Substitute x=9x = 9:

    Now substitute x=9x = 9 into the simplified expression:

    77(9)62+1=76362+1=71+1=71+1=72\frac{7}{\sqrt{7(9) - 62} + 1} = \frac{7}{\sqrt{63 - 62} + 1} = \frac{7}{\sqrt{1} + 1} = \frac{7}{1 + 1} = \frac{7}{2}

Final Answer:

limx97x621x9=72\lim_{{x \to 9}} \frac{\sqrt{7x - 62} - 1}{x - 9} = \frac{7}{2}

Would you like further details or have any other questions?


Here are 5 related questions:

  1. How do you recognize the indeterminate form of a limit problem?
  2. What are some other methods for solving limits besides rationalization?
  3. What happens if you don't cancel common factors in a limit problem?
  4. How does the conjugate method help in limit problems with square roots?
  5. How can you verify a limit using numerical methods?

Tip: Always check for factorable expressions or common terms in the numerator and denominator to simplify limits easily.

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Math Problem Analysis

Mathematical Concepts

Limits
Indeterminate Forms
Rationalization

Formulas

lim(x→a) f(x)/g(x) when both f(a) = 0 and g(a) = 0 (0/0 indeterminate form)
Difference of squares: (a^2 - b^2) = (a - b)(a + b)

Theorems

Difference of squares
Conjugate method in limits

Suitable Grade Level

Grades 11-12