what is sum of the first 20 terms of an A.P. ifa=4 and t20 = 36
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Given,
a= 4
20th term or last term for finding sum = 36
number of term = 20
Sum of n term =
(a + l) \times n \div 2(a+l)×n÷2
where
a= first term = 4
l = last term = 36
and n = no. of terms = 20
After substituting value
Sum = (4 + 36)X 20/2
= 40 X 10
= 400
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