Question

Find the sum of indicated number of terms in each of the following A.P.s
(i) 16, 11, 6 .....; 23 terms (ii) −0.5, −1.0, −1.5, .....; 10 terms
(iii) −1, 1/4, 3/2, .....,10 terms

Answer 1

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i) given AP = 16, 11, 6........
here a = 16
d = -5
n = 23
Sn = n/2 { 2a + ( n - 1 ) d }
= 23/2 { 2× 16 + ( 22 × (-5) ) }
= 11.5 ( 32 - 120 )
= 11.5 × (- 78 )
= - 897

ii) given AP = -0.5, -1.0, -1.5........
here a = - 0.5
d = - 0.5
n = 10
Sn = 10/2 { 2×(-0.5) + 9 × (-0.5) }
= 5 { -1 - 4.5 )
= 5 ( -5.5 )
= - 27.5

iii) given AP = -1, 1/4, 3/2.........
here a = -1
d = 5/4
n = 10
Sn = 10/2 { 2 × ( -1 ) + 9 × 5/4 }
= 5 { -2 + 11.25 }
= 5 × 9.25
= 46.25

Answer 2

Answer:

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