Question

find the sum of first 20 terms of ap 3,7,11,15......using formula
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Answer 1

Answer:

The 20th term of AP is

First term=3

common difference=a2-a1=7-3=4

To find 20th term,

a20= a+(n-1)d

a20=3+(20-1)4

a20=49

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Answer 2

Answer:

Step-by-step explanation:sum of 20 terms =20/2*2(5)+(20-1)4

=10*10+19(4)

=10*10+76

=10*86

=860