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Arithmetic Sequence

n= 5

a1= 4

a5=40

d=?

Solution: (Follow the formula above)

an=a1+(n-1)d

a5=4+(5-1)d

a5=4+(4)d

a5=4+4d

40-4=4d

36=4d

4d/4=36/4 (you need to copy the number to cancel 4 in 4d and make a fraction)

d=9

The answer is d=9

4+9=13

13+9=22

22+9=31

31+9=40

a₁ = 4

Formula/Rule:

an = 4 + (n-1) (9)

an = 4 + 9n - 9

an = 9n - 9 + 4

an = 9n - 5

To check:

a₅ = 45 - 5

a₅ = 40 (True)