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Calculus

Right-Hand Limit with Absolute Value at 7

Learn how a right-hand approach makes |x-7| positive, simplifies the fraction, and gives the one-sided limit of 1+|x-7|/(7-x).

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Problem

Evaluate

limx7+(1+x77x).\lim_{x \to 7^+}\left(1+\frac{|x-7|}{7-x}\right).

Step 1: Use the Approach Direction

Since x7+x \to 7^+, xx approaches 77 from the right. That means x>7x>7 while it gets closer and closer to 77.

Therefore,

x7>0.x-7>0.

Step 2: Simplify the Absolute Value

Because x7x-7 is positive, the absolute value does not change its sign:

x7=x7.|x-7|=x-7.

So the expression becomes

1+x77x.1+\frac{x-7}{7-x}.

Step 3: Rewrite the Denominator

Compare the numerator and denominator:

7x=(x7).7-x=-(x-7).

Therefore,

x77x=x7(x7)=1.\frac{x-7}{7-x} = \frac{x-7}{-(x-7)} = -1.

Step 4: Combine the Terms

So the expression simplifies to

1+(1)=0.1+(-1)=0.

Therefore,

limx7+(1+x77x)=0.\lim_{x \to 7^+}\left(1+\frac{|x-7|}{7-x}\right)=0.

Concepts

Concept of Limits

The limit of a function describes the value it approaches as the input gets closer to a particular number. One-sided limits approach from the left or right. A limit exists only when both one-sided limits are equal.

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