For sake of convenience, reverse the series, then it would be:
21,19,17.....7
a=21, d = -2,
s(4) = 4/2 (21+15)
s(4)=2(36)
s(4) = 72
For this case we must factor the following expression:

To factor, we must find two numbers that when added together give -7 and when multiplied by -10.
It is observed that there are not two whole numbers that comply with the aforementioned.
Thus, the following equation applies:

Where:

We replace:

So, the roots are:

Answer:

Answer:
22.8
Step-by-step explanation:

Answer:
2 11/15
Step-by-step explanation:
Let X equal the decimal number
Equation 1:
X=2.73¯¯¯(1)
With 1 digits in the repeating decimal group,
create a second equation by multiplying
both sides by 101 = 10
Equation 2:
10X=27.33¯¯¯(2)
Subtract equation (1) from equation (2)
10XX9X===27.33...2.73...24.6
We get
9X=24.6
Solve for X
X=24.69
Multiply to eliminate 1 decimal places.
Here you multiply top and bottom by 1 10's
= 101 = 10
24.69×1010=24690
Find the Greatest Common Factor (GCF) of 246 and 90, if it exists, and reduce the fraction by dividing both numerator and denominator by GCF = 6,
246÷690÷6=4115
Simplify the improper fraction,
=21115
In conclusion,
2.73¯¯¯=2 11/15
5,120........................................