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Question

Find a30a20 for the A.P 9,14,19,24,......

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Solution

Given A.P is
9,14,19,24,....
hence the common difference is given by d=an+1an
by putting n=1 in above equation
d=a2a1=(14)(9)
d=(14+9)
d=5
first term of this A.P is
a1=9
the nth term of this A.P is given by
an=a1+(n1)d
an=9+(n1)(5)
an=95n+5
an=45n.eq(1)


1) for finding the 30th term of sequence (a30) put n=30 in eq(1)
a30=45×30
a30=4150
a30=154

2) for finding the 20th term of sequence (a20)put n=20 in eq(1)
a20=45×20
a20=4100
a20=104


now,
a30a20=(154)(104)
a30a20=(154+104)
a30a2=50

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