Question

-81 is the ___ term of AP:21,18,15​

Answer 1

Answer:

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$- 81 = a + (n - 1)d \\ \\ - 81 = 21 + (n - 1) - 3 \\ \\ - 81 = 21 - 3n + 3 \\ \\ - 81 - 21 = - 3n + 3 \\ \\ - 102 - 3 = - 3n \\ \\ - 105 = - 3n \\ \\ 35 = n$

➡ -81 is the 35 term of the AP☺✨

Answer 2

Answer:

Hey...!!!

We know ,

nth term of an A.P is ..

tn = a+ (n-1)d

Here tn = -81

a = 21

d = -3

To find => n

So putting this values in formula we get....

-81 = 21 +( n-1) (-3)

-81 = 21 - 3n + 3

-3n + 3 = -81 -21

-3n + 3 = -102

-3n = - 105

Hence , n = 35

So, 35th term of the A.P would be -81...

Hope this helps....❤️❣️☺️