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## Answers

first term=6

common difference =6

by formula, sum of n terms=n/2[2a+(n-1)d]

1800=n/2[12+(n-1)6]

3600=n[12+6n-6]

3600=6n+6n

__²__

6n²+6n-3600=0

n²+n-600=0

n²+25n-24n-600=0

n(n+25)-24(n+25)=0

(n+25)(n-24)=0

so, n=24

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first term=6

common difference =6

by formula, sum of n terms=n/2[2a+(n-1)d]

1800=n/2[12+(n-1)6]

3600=n[12+6n-6]

3600=6n+6n

6n²+6n-3600=0

n²+n-600=0

n²+25n-24n-600=0

n(n+25)-24(n+25)=0

(n+25)(n-24)=0

so, n=24