How nany terms of an arithmetic sequence 6,10,14.... Needed to get sum 160?
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let n terms needed
Sum = n/2 ( 2a +(n-1) d)
where a is first term and d common difference
160 = n/2 ( 12 + (n-1)4)
320 = n ( 8 + 4n)
80 = 2n + n^2
n^2 + 2n -80 = 0
n^2 + 10 n -8n -80 = 0
n( n +10) -8( n+10) = 0
n = 8
Sum = n/2 ( 2a +(n-1) d)
where a is first term and d common difference
160 = n/2 ( 12 + (n-1)4)
320 = n ( 8 + 4n)
80 = 2n + n^2
n^2 + 2n -80 = 0
n^2 + 10 n -8n -80 = 0
n( n +10) -8( n+10) = 0
n = 8
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