If 21st term of an A.P is 25,find the sum of its first 41 terms.....
plzzz answer fast....
Answers
Answered by
1
Hola there...
According to the question,
a21 = 25
=> a + 20d = 25
We now have to find the sum of 41 terms so,
Sn = n/2 (2a + (n - 1)d)
=>S41. = 41/2 (2a + (41 - 1)d)
=> S41 = 41/2(2a + 40d)
=> S41 = 41(a + 20d)
=> S41 = 41 × 25
=> S41 = 1025. ....Ans
Hope this helps....:)
According to the question,
a21 = 25
=> a + 20d = 25
We now have to find the sum of 41 terms so,
Sn = n/2 (2a + (n - 1)d)
=>S41. = 41/2 (2a + (41 - 1)d)
=> S41 = 41/2(2a + 40d)
=> S41 = 41(a + 20d)
=> S41 = 41 × 25
=> S41 = 1025. ....Ans
Hope this helps....:)
Answered by
2
25 =a+20d: 50=4a+40d
S(41)= (41/2)[2a+40d]
S41=20.5[50]=1025
S(41)= (41/2)[2a+40d]
S41=20.5[50]=1025
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