Question

EXAMPLES Let f (x) be a function defined by f (x)
4x-5 , if x 2
x-2, if x > 2
Find , if lim f() exists.
X-2​

Answer 1

Answer:

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Using the definition of the limit, limx→a f(x), we can derive many general laws of limits, that help us to

calculate limits quickly and easily. The following rules apply to any functions f(x) and g(x) and also

apply to left and right sided limits:

Suppose that c is a constant and the limits

limx→a

f(x) and limx→a

g(x)

exist (meaning they are finite numbers). Then

1. limx→a[f(x) + g(x)] = limx→a f(x) + limx→a g(x) ;

(the limit of a sum is the sum of the limits).

2. limx→a[f(x) − g(x)] = limx→a f(x) − limx→a g(x) ;

(the limit of a difference is the difference of the limits).

3. limx→a[cf(x)] = c limx→a f(x);

(the limit of a constant times a function is the constant times the limit of the function).

4. limx→a[f(x)g(x)] = limx→a f(x) · limx→a g(x);

(The limit of a product is the product of the limits).

5. limx→a

f(x)

g(x) =

limx→a f(x)

limx→a g(x)

if limx→a g(x) 6= 0;

(the limit of a quotient is the quotient of the limits provided that the limit of the denominator is

not 0)

Example If I am given that

limx→2

f(x) = 2, limx→2

g(x) = 5, limx→2

h(x) = 0.

find the limits that exist (are a finite number):

(a) limx→2

2f(x) + h(x)

g(x)

=

limx→2(2f(x) + h(x))

limx→2 g(x)

since limx→2

g(x) 6= 0

=

2 limx→2 f(x) + limx→2 h(x)

limx→2 g(x)

=

2(2) + 0

5

=

4

5

(b) limx→2

f(x)

h(x)

(c) limx→2

f(x)h(x)

g(x)