If a temperature increases by (2x + 1)ºc from the original x, in x + 5 seconds, then the average rate of change is (x - 3) c/s.
which is a possible value of x?
a) 2
b)4
c)8
d)16

A possible value of x = B)4

The main composition of algebraic expressions are:

algebraic forms separated by arithmetic operations

consists of one phrase (monomial) to many phrases (polynomial)

is a value that can be changed, can be in the form of letters, for example, x, y, a, b, etc.

is a fixed value, can be a number

+, -,:, x

The Average Rate of Change of a function shows the comparison between 2 objects that change

If we use the notation function, the Average rate of Change of a function from a to b can be formulated as:

ROC = rate of change

a temperature increases by (2x + 1) ºC from the original x, in x + 5 seconds, then the average rate of change is (x - 3) C / s.

There are 2 functions that change, temperature and time

If we change above statement to algebraic form, it becomes

6 squared divided by 2 (3) +4  

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an algebraic expression  

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what is the question here. i think you messed up.