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Arithmetic progression

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Question

 Let a1,a2,a3,.,a49 be in A.P. such that k=012a4k+1=416 and a9+a43=66 . If a12+a22+.+q172=140m , then m is equal to 

Difficult
Solution

[SolutionStep1]:

 Let a1,a2,a3,,a49 be in A.P 

 Let ' d ' be the common difference 

[SolutionStep2]:

 Given k=012a4k+1=416

a1+a5+a9+....+a49=416

 Here n=13 , common difference D=4d

[SolutionStep3]:

Sn=n22a+n1D

1322a1+124d=416

a1+24d=32.................1

 Given a9+a43=66

a1+8d+a1+42d=66

a1+25d=33..............2

21d=1

 From (1),a1=8

[SolutionStep4]:

 Let a12+a22+.+a172=S

82+92+..+(24)2=S  a17=a1+16d=8+16(1)=24

S=12+22+..+72+82+92+.+(24)2-12+22+.+72

=(24)(25)(49)6-7(8)(15)6  n2=n(n+1)(2n+1)6

=1629400840

=4760

=14034

m=34


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