Question

The 5th term of an ap is 26 and the 10th term is 51.find 15th term of an ap

Answer 1

Hey user here is your answer......

---->Given----

a5=26

a10=51

So,
◆a+(n-1)d=26

◆a+(5-1)d=26

◆a+4d=26----------(1)

Similarly,

◆a+9d=51-------(2)

Subtract equation 2 from 1

a+9d=51
a+4d=26
- -. -
So,5d=25

d=25/5=5

◆Now put value of d in equation(1)

◆a+4(5)=26

◆a+20=26

◆a=26-20=6

Now, a15=a+(15-1)d

So, a15=6+14(5)
\a15=6+70
◆a15=76

Thanks☺️

Answer 2

Hey......

a+4d=26
a=26 -4d------1

a +9d =51

now putting the value of a we get...

26-4d +9d=51
5d=51-26
5d=25
d =5

then a =26 -4d
a=26 -4×5
a =26-20
a=6

Now 15th term =a+14d
=6+14×5
=6+70=76

Hope this helps....

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