find the sum 3^2 + 6^2 + 9^2+... + 30^2.
AP
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Step-by-step explanation:
A.P. :- 3² + 6² + 9².............. + 30²
9 + 36 + 81.........+ 900
a=9
a2=36
d=a2-a1
=36-9
= 27
an= a+(n-1)d
900= 9+(n-1)27
900-9=(n-1) 27
891/27= n-1
33 = n-1
n= 33+1
n= 34
Sn = n/2{a + an}
= 34/2{9+900}
= 17{ 909}
= 15, 453
So the sum of an A.P. = 15,453
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