if three arithmetic means are inserted between -15 and 9,find the first of these arithmetic means.

Sagot :

Add -15 and 9, then divide by 2.

The result is -6/2 = -3

-15, ____, -3, _____, 9

Add -15 and -3, then divide by 2

The result is -18/2 = -9

The common difference:
-9 - (-15) = -9 + 15 = 6

So, add 6 to -15, =-9
      add 6 to -9 =  -3
       add 6 to -3 = 3
       
These are the three missing terms between  -15 and 9.

-15, -9, -3, 3, 9

The first of the arithmetic means is -9.

Hmmmm.

-15 _ _ _ 9
There are 5 numbers
First you will find the d or the common difference
The formula is
An=A1 + (n-1)d
A5= -15 + (5-1)d
9 = -15 + 4d
9+15 =4d
24=4d
Divided both by 4
6 = d

Then add it

A1 =-15
A2=-15+6 =-9
A3=-9 + 6=-3
A4=-3 + 6 = 3
A5= 3 + 6 = 9
Then the sequence is -15, -9, -3, 3, 9



I hope it helps...