Exercise 18 Page 711

We want to find the arithmetic means in the given arithmetic sequence. To do so, we first have to find the value of the common difference d. 72, , , , 24 We see that the first term is a_1= 72 and there are 5 total terms. Therefore, we have that n= 5. We can substitute these two values in the general formula for the nth term of an arithmetic sequence. a_n= a_1+( n-1)d ⇓ a_5= 72+( 5-1)d We are also given the value of the last term, 24. Since n=5, we have that a_5=24. Let's substitute this into our formula and solve for d. We will use the common difference to calculate the five arithmetic means.

The arithmetic means are 60, 48, and 36.