Answer:
Sum of the sequence (Sn) = 33,859
Step-by-step explanation:
Given:
Sequence = 685+678+671+664+...+6
Find:
Sum of the sequence (Sn)
Computation:
a = 685
d = 678 - 985 = -7
an = 6
an = a+(n-1)d
6 = 685+(n-1)(-7)
-679 = (n-1)(-7)
97 = n-1
n = 98
So,
Sum of the sequence (Sn) = (n/2)[a+an]
Sum of the sequence (Sn) = (98/2)[685+6]
Sum of the sequence (Sn) = (49)(691)
Sum of the sequence (Sn) = 33,859
The number of handshakes that will occur in a group of eighteen people if each person shakes hands once with each other person in the group is 153 handshakes
In order to determine the number of handshakes that will occur among 18 people, that is, the number of ways we can choose 2 persons from 18 people.
∴ The number of handshakes = 






∴ The number of handshakes = 153 handshakes
Hence. 153 handshakes will occur in a group of eighteen people if each person shakes hands once with each other person in the group.
Learn more here: brainly.com/question/1991469
Yes it is,
it is reflection like a mirror, but, it copy's the position and moves it upward