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What are the domain and range of the function [tex]\( f(x) = 3^x + 5 \)[/tex]?

A. Domain: [tex]\((-\infty, \infty)\)[/tex]; Range: [tex]\((0, \infty)\)[/tex]

B. Domain: [tex]\((-\infty, \infty)\)[/tex]; Range: [tex]\((5, \infty)\)[/tex]

C. Domain: [tex]\((0, \infty)\)[/tex]; Range: [tex]\((-\infty, \infty)\)[/tex]

D. Domain: [tex]\((5, \infty)\)[/tex]; Range: [tex]\((-\infty, \infty)\)[/tex]


Sagot :

To determine the domain and range of the function [tex]\( f(x) = 3^x + 5 \)[/tex], we'll analyze the properties of the function step-by-step:

### Domain

1. Definition of the Exponential Function:
The function [tex]\( 3^x \)[/tex] is defined for all real numbers [tex]\( x \)[/tex]. This means you can plug any real number into [tex]\( 3^x \)[/tex] and get a valid output.

2. Adding a Constant:
Adding the constant 5 to [tex]\( 3^x \)[/tex] doesn't change the fact that [tex]\( 3^x \)[/tex] is defined for all real numbers [tex]\( x \)[/tex].

Given these points, the domain of [tex]\( f(x) = 3^x + 5 \)[/tex] is all real numbers:
[tex]\[ \text{Domain}: (-\infty, \infty) \][/tex]

### Range

1. Behavior of the Exponential Function:
The function [tex]\( 3^x \)[/tex] is an exponential function, and its range is [tex]\( (0, \infty) \)[/tex] because [tex]\( 3^x \)[/tex] is always positive for any real [tex]\( x \)[/tex] and can get arbitrarily large as [tex]\( x \)[/tex] increases and arbitrarily close to 0 as [tex]\( x \)[/tex] decreases.

2. Adding a Constant:
Adding 5 to [tex]\( 3^x \)[/tex] shifts the entire graph of [tex]\( 3^x \)[/tex] upwards by 5 units. This transformation affects the range as follows:
- The minimum value of [tex]\( 3^x \)[/tex] is just above 0 (when [tex]\( x \)[/tex] goes to [tex]\(-\infty\)[/tex]), so [tex]\( 3^x + 5 \)[/tex] will be just above 5.
- There is no upper bound to the values of [tex]\( 3^x + 5 \)[/tex] since [tex]\( 3^x \)[/tex] can become arbitrarily large.

Therefore, the range of [tex]\( f(x) = 3^x + 5 \)[/tex] is:
[tex]\[ \text{Range}: (5, \infty) \][/tex]

### Conclusion

Combining the domain and range, the correct option is:
[tex]\[ \text{Domain}: (-\infty, \infty) \][/tex]
[tex]\[ \text{Range}: (5, \infty) \][/tex]

So, the answer to the question is:
- [tex]\(\text{domain: } (-\infty, \infty)\)[/tex]
- [tex]\(\text{range: } (5, \infty)\)[/tex]