
Calculating Limits Using the Limit Laws

tarix  20.09.2018  ölçüsü  0,64 Mb.   #70005 

In this section we use the following properties of limits, called the Limit Laws, to calculate limits.
Calculating Limits Using the Limit Laws These five laws can be stated verbally as follows: Sum Law 1. The limit of a sum is the sum of the limits. Difference Law 2. The limit of a difference is the difference of the limits. Constant Multiple Law 3. The limit of a constant times a function is the constant times the limit of the function.
Calculating Limits Using the Limit Laws Product Law 4. The limit of a product is the product of the limits. Quotient Law 5. The limit of a quotient is the quotient of the limits (provided that the limit of the denominator is not 0). For instance, if f (x) is close to L and g (x) is close to M, it is reasonable to conclude that f (x) + g (x) is close to L + M.
Example 1
Example 1(a) – Solution From the graphs of f and g we see that and Therefore we have
Example 1(b) – Solution We see that limx 1 f (x) = 2. But limx 1 g (x) does not exist because the left and right limits are different: So we can’t use Law 4 for the desired limit. But we can use Law 4 for the onesided limits: The left and right limits aren’t equal, so limx 1 [f (x)g (x)] does not exist.
Example 1(c) – Solution and Because the limit of the denominator is 0, we can’t use Law 5. The given limit does not exist because the denominator approaches 0 while the numerator approaches a nonzero number.
Calculating Limits Using the Limit Laws If we use the Product Law repeatedly with g(x) = f (x), we obtain the following law. In applying these six limit laws, we need to use two special limits: These limits are obvious from an intuitive point of view (state them in words or draw graphs of y = c and y = x).
Calculating Limits Using the Limit Laws If we now put f (x) = x in Law 6 and use Law 8, we get another useful special limit. A similar limit holds for roots as follows. More generally, we have the following law.
Calculating Limits Using the Limit Laws Functions with the Direct Substitution Property are called continuous at a.
In general, we have the following useful fact.
Calculating Limits Using the Limit Laws Some limits are best calculated by first finding the left and righthand limits. The following theorem says that a twosided limit exists if and only if both of the onesided limits exist and are equal. When computing onesided limits, we use the fact that the Limit Laws also hold for onesided limits.
Calculating Limits Using the Limit Laws
Calculating Limits Using the Limit Laws The Squeeze Theorem, which is sometimes called the Sandwich Theorem or the Pinching Theorem, is illustrated by Figure 7. It says that if g (x) is squeezed between f (x) and h (x) near a, and if f and h have the same limit L at a, then g is forced to have the same limit L at a.
Dostları ilə paylaş: 

