Question

If 1 + 5 + 9 +13+...+ x = 780, then the value of xis
O 67
O 73
O 77
O 83​

Answer 1

Answer:

answer is 83

Step-by-step explanation:

your question is this

so add 1 +5 +9 +13=28

x=83

Answer 2

Answer:

77 is the correct answer

Sn=n(2a+(n-1)d/2 [1]

an=a+(n-1)d. [2]

Sn=780

a=1

d=4

an=x

from [1]

if you simplify by inserting it's values you will get an equation. 2n^2-n-780=0.

if you find the zeros of the polynomial the zeros are 20 and -39/2 as the n value can't be in negative the zero is 20.

as n is 20

substitute n value in 2 equation

x=1+(20-1)4

x=1+(19)4

x=1+76

x=77