find the sum of the a.p. -4,-1,+2,+5,+.....+56
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1
Answer:
546
Step-by-step explanation:
As per the question;
a = -4,
d = 3
an = a + (n - 1)d
=> 56 = -4 + (n - 1)3
=> 56 + 4 = (n - 1)3
=> 60/3 = n - 1
=> 20 = n - 1
=> n = 21
Formula for addition of terms in AP : Sn = n/2(2a + (n - 1)d)
=> 21/2(2(-4) + (21 - 1)3) = Sn
=> 21/2(-8 + (20)3) = Sn
=> 21(-4 + (10)3) = Sn
=> 21(-4 + 30) = Sn
=> 21(26) = Sn
=> 546 = Sn
Hoping that it helped...
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