# For Which of the Following Functions Is F(a + B) = F(a) + F(B) For All Positive Numbers a and B ?

For Which of the Following Functions Is F(a + B) = F(a) + F(B) For All Positive Numbers a and B?

Functions play a crucial role in mathematics, serving as a tool to describe relationships between different variables. One important property of functions is the ability to combine or manipulate them using various operations. In this article, we will explore the concept of a function that satisfies the equation F(a + B) = F(a) + F(B) for all positive numbers a and B. We will examine different types of functions and determine which ones meet this criterion. Additionally, a FAQs section will be provided to address common questions related to this topic.

The equation F(a + B) = F(a) + F(B) represents an important property of functions known as additivity. It states that the value of the function applied to the sum of two numbers is equal to the sum of the function values applied to each individual number. To determine which functions satisfy this equation for all positive numbers a and B, we will consider several cases.

1. Linear Functions:
A linear function is defined as f(x) = mx + b, where m and b are constants. By substituting a + B for x in the equation, we get F(a + B) = m(a + B) + b. Expanding this expression, we obtain F(a + B) = ma + mB + b. On the other hand, F(a) + F(B) = ma + b + mB + b. By comparing these two expressions, we observe that they are not equal unless mB = mB, which implies that m must be zero. Therefore, the only linear function that satisfies the equation is f(x) = b, where b is a constant.

2. Exponential Functions:
An exponential function is defined as f(x) = ab^x, where a and b are constants. By substituting a + B for x in the equation, we get F(a + B) = ab^(a + B). On the other hand, F(a) + F(B) = ab^a + ab^B. To determine if these expressions are equal, we need to examine the properties of exponentiation. Since b^(a + B) = b^a * b^B, we can rewrite F(a + B) as ab^a * b^B. By comparing this expression to F(a) + F(B), we observe that they are equal if and only if b^B = b^B. Therefore, any exponential function with a constant base b satisfies the equation.

3. Logarithmic Functions:
A logarithmic function is defined as f(x) = log_b(x), where b is the base of the logarithm. By substituting a + B for x in the equation, we get F(a + B) = log_b(a + B). On the other hand, F(a) + F(B) = log_b(a) + log_b(B). To determine if these expressions are equal, we need to examine the properties of logarithms. We know that log_b(a * B) = log_b(a) + log_b(B), which implies that F(a) + F(B) can be rewritten as log_b(a * B). By comparing this expression to F(a + B), we observe that they are equal if and only if a * B = a + B. This equation is only true when a = 1 or B = 1. Therefore, logarithmic functions with a base other than 1 do not satisfy the equation.

FAQs:

Q: Are there any other types of functions that satisfy the equation F(a + B) = F(a) + F(B)?
A: Yes, there are other types of functions that satisfy the equation. Some examples include polynomial functions, trigonometric functions, and constant functions. However, these functions may have additional requirements or constraints that need to be considered.

Q: Can a function satisfy the equation for some positive numbers a and B but not for others?
A: No, for a function to satisfy the equation F(a + B) = F(a) + F(B) for all positive numbers a and B, it must hold true for any combination of positive numbers. If there exist some values of a and B for which the equation is not satisfied, then the function does not meet the criterion.

Q: Is it possible for a function to satisfy the equation if a and B are not positive numbers?
A: The equation F(a + B) = F(a) + F(B) is specifically defined for positive numbers a and B. If a function satisfies this equation for any other type of numbers, it may be subject to additional conditions or requirements.