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10 questions from this quiz
Adding all terms in a sequence
un=a+(n−1)du_n = a + (n-1)dun=a+(n−1)d
Sum of first nnn terms
Sn=n2[2a+(n−1)d]S_n = \frac{n}{2}[2a + (n-1)d]Sn=2n[2a+(n−1)d]
10,40010,40010,400
a+2d=72a + 2d = 72a+2d=72
Sn=n2[a+l]S_n = \frac{n}{2}[a + l]Sn=2n[a+l]
Using S59−S21S_{59} - S_{21}S59−S21
393939
444444
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