Question

The nth term of sequence 21,42,63......Is 420 .Find n

Answer 1

Answer:

Value of n is 20.

Step-by-step explanation:

From the identities of arithmetic progressions,

xth term = a + ( x - 1 )d

∴ nth term = a + ( n - 1 )d

Given sequence : 21 , 42 , 63 .... 420.

In the sequence,

Fist term = a = 21

Common Difference = 42 - 21 = 21

According to the question

nth term of the AP = 420

⇒ a + ( n - 1 )d = 420

⇒ 21 + ( n - 1 )21 = 420

⇒ ( n - 1 )21 = 420 - 21

⇒ ( n - 1 )21 = 399

⇒ ( n - 1 ) = 399 / 21

⇒ ( n - 1 ) = 19

⇒ n = 19 + 1

⇒ n = 20

Thus,

420 is the 20th term of the AP and value of n is 20.

Answer 2

Hii !!



AP = 21 , 42 , 63 ,......420




Here,


first term ( a ) = 21


Common difference ( d ) = 42 - 21 = 21



Last term ( Tn ) = 420



a + ( n - 1 ) × d = 420



21 + ( n - 1 ) × 21 = 420




21 + 21n - 21 = 420



21n = 420



n = 20