Question

The sum of 7 numbers in a.P. Is 42 and the sum of their squares is 364. Find the 7th number.

Answer 1

Answer:

Let 5 numbers in anA.P.are a-2d ,a-d, a,a+d and a+2d.

Acordingly:-

a-2d+a-d+a+a+d+a+2d=25

5a=25

a=5………….(1)

(a-2d)^2+(a-d)^2+a^2+(a+d)^2+(a+2d)^2=165

5a^2+10d^2=165 , put a=5

125+10d^2=165

10d^2=40

d^2=4

d=+/-2

1st NO =5–2(+/-2)=1 or 9

2nd NO=5-(+/-2)= 3 or 7

3rd NO =5 = 5 or 5

4th NO =5+(+/-2)=7 or 3

5th NO=5+2(+/-2) =9 or 1 ,Answer

Answer 2

I don't know the solution