In an AP is an = 2–3. Find the sum of first 12 terms.
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Use the formula to find sum of AP up to n terms
where a is the first term, d is the common difference, n is the number of terms.
So, 11/2(2a+10d) = 19/2(2a+18d)
22a+110d=38a+342d
16a=-232d
a=-14.5d
Now sum of first 30 terms
=30/2(2a+29d)
=15(29d- 29d) = 0
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