# maths

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find a6 for an arithmetic sequence where a1=3x+1 and d=2x+6.

2.A display of cans on a grocery shelf consists of 20 cans on the botton, 18 cans inthe next row, and so on in an arithmic sequence, until the to[p row has four cans. how many cans , in total, are in the display?

• maths -

a = 3x+1
d = 2x+6

term(6) = a + 5d
= 3x+1 + 5(2x+6)
= 13x + 31

2.

a = 20
d = -2
term(n) = 4
4 = a + (n-1)d
4 =20 - 2(n-1)
4 = 20 - 2n + 2
2n = 18
n = 9

sum(9) = (9/2)(first + last)
= (9/2)(20+4) = 108

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