Answers

2016-06-17T15:15:18+08:00

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
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  • Brainly User
2016-06-17T16:23:50+08:00
D = 9 
a₁ = 4

Formula/Rule:

an = 4 + (n-1) (9)
an = 4 + 9n - 9
an = 9n - 9 + 4
an = 9n - 5

ANSWER:   a_{n} = 9n - 5

To check:
a₅ = 40   n = 5

an = 9n - 5
a₅ = 9(5) - 5 
a₅ = 45 - 5
a₅ = 40  (True)  
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