18. The 8th term of an A. P. is zero. Prove that 38th term is triple of its 18th term.

34.The 24th term of an AP is twice its 10th term. Show that its 72nd term is the 4 times its 15th term

@Both: Good attempt. Keep it up!

@Aparna: Good to know that you got your answer.

  • -4

since the eighth term of an AP is 0

.'.  a8=o

a+7d=0

a=-7d

L.H.S. = a38

 

=a+37d

=-7d+37d

=30d

 

 

R.H.S.=

3(a18)

=3(a+17d)

=3(-7d+17d)

=3(+10)

=30d.

Since , L.H.S = R.H.S. Therefore proved a38=3(a18).

  • 16

1. a8=0

a+7d=0  ,   a=-7d

a38=a +37d     ,    a18=a+17d

a38=-7d+37d = 30d    ,    a18=-7d +17d= 10d

30d=3(10d)

Therefore, a38= 3( a18)

  • 4

2.  a24=a +23d  ,  a10=a + 9d

a+23d=2(a+9d)

a+23d=2a+18d

2a-a=23d-18d

a=5d

Now,  a72=a+71d   ,  a15=a+14d

a+71d=5d+71d=76d (Since a=5d)

Similarly, 

4(a15)=2(a+14d)

=4(5d+14d)

=4(19d)

=76d

Therefore, 

 a72=4(a15)

  • 6

thnx ppl !
i gave you thumbs as reward! :)

  • -1
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