Question

Find 20th term from the end of an A.P. 3,7,11..... 407.

Answer 1

Solution :

Given A.P : 3,7,11,...,407

first term ( a ) = 3 ,

common difference ( d ) = a2 - a1

= 7 - 3

= 4

Now ,

Rearranging the sequence in reverse order,

we get

407 , 404 , 401 , ...., 11, 7 , 3

Here ,

first term ( a ) = 407 ,

common difference ( d ) = -4

n = 20

nth term ( an ) = a + ( n - 1 )d

= 407 + ( 20 - 1 )(-4)

= 407 - 19 × 4

= 407 - 76

= 331

Therefore ,

20th term in given A.P = 331

••••

Answer 2

Answer:

Step-by-step explanation:

In a Given A.P ;

a = 3

d = 7-3 = 4

On the contrary let 144 be the nth term of A.P

Tn = 144

n = ?

Tn = a+(n-1)d

144 = 3+(n-1)4

n-1 = 141/4

n = 35.25+1

n = 36.25

As the value of n is a decimal or number, hence 144 is not the term of given A.P