Question

in an arithmetic progression, nth terms is 2.1 less then the 11th terms the common difference of -0. 7 find the value of n​

Answer 1

Answer:

14

Step-by-step explanation:

Given common difference d = -0.7

We know that,

$a_{n}$ = a + (n-1)*d

and $a_{11}$ = a + 10*d

Given,

$a_{11} - a_{n} = 2.1$ (according to the condition)

⇒ a + 10*d - (a + (n-1)*d) = 2.1

⇒ a + 10*d - a - (n-1)*d = 2.1

⇒ 10*d -(n-1)*d = 2.1

⇒ 10*d - n*d + d = 2.1

⇒ 11*d - n*d = 2.1

Take d common

⇒d(11 - n) = 2.1

⇒(-0.7)*(11 - n) = 2.1          since d = -0.7

⇒11 - n = 2.1/(-0.7)

⇒11 - n = -3

⇒11 + 3 = n

∴ n = 14