Question

f the common differences of
then anot
an AP is 3,
15 is​

Answer 1

Answer:

Let a be the first term of an A.P. and common difference be 3.So,a15=a+(15−1)d

⇒a15=a+14dAnd,

⇒a9=a+(9−1)d

⇒a9=a+8d

On subtracting

a15−a9=(a+14d)−(a+8d)=6d=6×3=18

⇒a15−a9=18

Step-by-step explanation:

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Answer 2

Given: d=3

We know:

a

n

=a+(n−1)d

∴a

20

−a

15

=[a+19d]−[a+14d]

=5d

=5×3

=15