How can expressions be written and evaluated to solve for unknowns in the real world?
Writing expressions requires figuring out which quantity in a situation is unknown, and define a variable to represent that quantitiy.
We look for words in the problem that will help us out what kind of operation to use in a given situation.
Example:
Donna bought 5 chocolate bars, and then ate some. Write an expression to represent how many chocolate bars Donna has left.
If we let the variable c represent the number of chocolates Donna has eaten, then we can write the expression on how many bars Donna has left as: 5 - c
Answer:

Step-by-step explanation:
Arithmetic sequence:
In an arithmetic sequence, the difference between consecutive terms is always the same, and is called common difference.
The nth term is given by the following equation:

In which
is the first term and d is the common difference.
First term is 9 common difference is -2
This means that 
So, the nth term is given by:



Answer:
No solution
Step-by-step explanation:
This is a geometric sequence since there is a common ratio between each term. In this case, multiplying the previous term in the sequence by 2 gives the next term. In other words, <em>a n +a1 ⋅ r n -1</em><em> </em>
Geometric Sequence:<em> </em><em>r = 2</em>
The series given has a value of<em> </em><em>r </em>such that <em>r > 1 or
r < − 1.</em> Therefore, the infinite sum cannot be calculated.<em>
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