The nth term of sequence 21,42,63......Is 420 .Find n
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2
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.
Answered by
7
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
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
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