Combination Theorem for Sequences/Real/Difference Rule

Theorem
Let $\sequence {x_n}$ and $\sequence {y_n}$ be sequences in $\R$.

Let $\sequence {x_n}$ and $\sequence {y_n}$ be convergent to the following limits:


 * $\ds \lim_{n \mathop \to \infty} x_n = l$
 * $\ds \lim_{n \mathop \to \infty} y_n = m$

Then:
 * $\ds \lim_{n \mathop \to \infty} \paren {x_n - y_n} = l - m$

Proof
From Sum Rule for Real Sequences:


 * $\ds \lim_{n \mathop \to \infty} \paren {x_n + y_n} = l + m$

From Multiple Rule for Real Sequences:
 * $\ds \lim_{n \mathop \to \infty} \paren {-y_n} = -m$

Hence:
 * $\ds \lim_{n \mathop \to \infty} \paren {x_n + \paren {-y_n} } = l + \paren {-m}$

The result follows.

Also see

 * Sum Rule for Real Sequences