I think it is 9 - x because 81-x^2/9-x = 9-x
Answer: 
Step-by-step explanation:
You can reduce the fractions, then:



Rewrite them as following:

If you subtract the first number and the second number, you obtain:

If you subtract the second number and the second number, you obtain:

Therefore, you must subtract
and
to obtain the number asked. Then, this is:

I think hamburger and French fries
Current year is 2016
born year is 1977
old
2016 - 1977
39 years
Answer:

Step-by-step explanation:
The sum you are trying to understand is this.

Remember that in general when you have a geometric series
you have that
and that equality is true as long as
.
Therefore here we have
and 
Therefore we can use the formula and
