in a A.P first two terms are -3,4 then find t21 and s21
Answers
Answered by
1
Answer:
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Explanation:
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Answered by
1
Answer:
t21= 137
s21= 2877
Explanation:
t21= a1 + 20d
= -3 + 20 x 7
= -3 +140
= 137
s21 = n/2 [ 2a + (n-1)d]
= 21/2 [2x(-3) + (21-1) 7]
= 21 [-3 + 20 x 7]
= 21 [-3 + 140]
= 21 x 137
= 2877
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