1.

The nth ,term of an AP is an=5n-3, find the sum of the first 20 term​

Answer»

Hello mate here is your perfect answer
let n=1
a1=5(1)-3=2 .......(first term)
Let n=2
a2=5(2)-3=7 .........(second term)
Now,
d=a2-a1=7-2=5 ....(COMMON difference)
Now,
S20=20/2(2a+(20-1)d)
S20=10(2(2)+19(5))
S20=10(99)
S20=990

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