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10 questions from this quiz
Adding all terms in a sequence together
Sum of first nnn terms of a series
Sn=n2[2a+(n−1)d]S_n = \frac{n}{2}[2a + (n-1)d]Sn=2n[2a+(n−1)d]
212121
a+2d=72a+2d=72a+2d=72 and a+7d=37a+7d=37a+7d=37
Using S59−S21S_{59} - S_{21}S59−S21
393939
Last term being summed
u1=7u_1=7u1=7, u2=9u_2=9u2=9
444444
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