Question

Find the 17th term from the last of an Ap 3,15,27,....243
​

Answer 1

Answer:

a=243

d=-12

a17=a+16d

=243+16×-12

243-192

= 51

Answer 2

$\underline\red{\bold{ANSWERE}}$

The 17th term from the la st is 51

______________________________________

${\bold{\boxed{\sf{\green{GIVEN \: \: that}}}}}</p><p></p><p>$

• There is an Ap.

• Ap = 3,15,27,________243

______________________________________

$\underline\red{\bold{TOFIND}}$

• What is the 17th term of this Ap from the la st?

____________________________________

$\underline\red{\bold{FORMULA}}$

• nth term of an Ap = a +(n-1)d

where,

• a = first term of Ap

• n = total number of an Ap

• d = diffrence between two term

______________________________________

$\underline\red{\bold{SOLUTION}}$

Ap = 3,15,27,_______243

d = 15-3 = 12

first term of Ap "a" = 3

la st term of Ap "an" = 243

• Total number of term =

$an = \: a + (n - 1)d \\ = > 243 = 3 + (n - 1)12 \\ = > (n - 1)12 =243 - 3 \\ = > n - 1 = \frac{240}{12} \\ = > n = 20 + 1 = 21$

So total number of term(n) = 21

• From la st 17th term will be 5th term from the start

Now the 17th term from the last

$a5 = a + 4d = 3 + 4 \times 12 \\ a5 = 3 + 48 = 51$

______________________________________

$\blue{\texttt{your answer}}$

The 17th term from the last is 51 .