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Exercise 12.1 · Q12

Q.lim⁡x→−21x+12x+2\lim_{x\to -2}\dfrac{\frac{1}{x} + \frac{1}{2}}{x + 2}

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Combine the fractions in the numerator over a common denominator, then cancel the (x+2)(x+2) factor that appears in both numerator and denominator. The limit evaluates to −14-\frac{1}{4}.

This limit initially presents an indeterminate form 00\frac{0}{0} when we substitute x=−2x = -2 directly. The numerator 1x+12\frac{1}{x} + \frac{1}{2} becomes 1−2+12=0\frac{1}{-2} + \frac{1}{2} = 0, and the denominator is also 00. This signals that both numerator and denominator share a common factor of (x+2)(x+2), which we need to cancel algebraically before evaluating the limit.

The key insight is to recognize that the complex fraction in the numerator can be simplified by finding a common denominator. Once we do that, the (x+2)(x+2) factor will reveal itself.

Step-by-step solution:

  1. Combine the fractions in the numerator over the common denominator 2x2x:

1x+12=22x+x2x=2+x2x\frac{1}{x} + \frac{1}{2} = \frac{2}{2x} + \frac{x}{2x} = \frac{2 + x}{2x}

  1. Rewrite the entire expression as a division of fractions:

1x+12x+2=2+x2xx+2=2+x2x⋅1x+2\frac{\frac{1}{x} + \frac{1}{2}}{x + 2} = \frac{\frac{2+x}{2x}}{x+2} = \frac{2+x}{2x} \cdot \frac{1}{x+2}

  1. Notice that 2+x=x+22 + x = x + 2, so we can cancel this common factor: 2+x2x(x+2)=x+22x(x+2)=12x\frac{2+x}{2x(x+2)} = \frac{x+2}{2x(x+2)} = \frac{1}{2x} …

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