Math, asked by girianushu, 1 day ago

The fifth and twelve terms of an A.P. are respectively 17 and 45. Find the sum of the first 15 terms of the progression

Answers

Answered by adityagodase84

2

Step-by-step explanation:

t5 = a+4d

17 = a+4d

a=17-4d... 1

t12=a+11d

45=a+11d

a= 45-11d...2

from 1 and 2,

17-4d=45-11d

7d=28

d=4

a=17-4d

=17-16

a=1

Sn= n/2 *[2a+(n-1) d)

S15= 15/2 * [2+14*4]

= 15/2*58

= 15*29

=435

hope it's help you

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