Question

The sum of the first 15 term
s of the A. P. 21, 18, 15​

Answer 1

Answer:

0

Step-by-step explanation:

Sum=15/2(2*21+(15-1)-3)

=15/2(42+(-42))

=15/2*0

=0

Answer 2

Answer:

0

Step-by-step explanation:

as Sn = n/2 (2a+(n-1)d)

Here a= 21; d= -3, n= 15

S15 = (15/2)((2×21) + (15-1)(-3))

or

(15/2)(42-42)

or

(15/2)(0)

or

0.

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