ICSE & CBSE Board Question Based on Arithmetic Progression of RS Aggarwal.
Here you have to find the sum of first nth terms.
This is the Question Number 3 Of Exercise 11 C of RS Aggarwal Solution.
Deepak BoraNewbie
Find the sum of first 18 terms of the AP 9, 7, 5, 3,…..
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Here
a = 9
d = 7 – 9
= -2
S18 = n/2( 2a + (n – 1) d
= 18/2(2 × 9 + (18-1) × -2
= 9 (18 + (-34)
= 9 × (-16)
= -144