In: Advanced Math
For the following exercises, find the specified term given two terms from an arithmetic sequence.
a1 = 33 and a7 = −15. Find a4 .
Consider an arithmetic sequence with a1 = 33 and a7 = -15
Use the formula for nth term of an arithmetic sequence,
an = a1 + (n – 1)d ...... (1)
Substitute a1 = 33, n = 7 and a7 = -15 in formula (1),
-15 = 33 + (7 – 1)d
-15 = 33 + 6d
6d = -15-33
6d = 48
Division by 6 gives,
d = -48/6
d = -8
Compute forth term a4 of given sequence, substitute a1 = 33 and d = -8 in equation (1),
a4 = 33 + (4 – 1) × (-8)
= 33 + 3 × (-8)
= 33 – 24
= 9
Therefore, fourth term of given arithmetic sequence is a4 = 9.
Therefore, fourth term of given arithmetic sequence is a4 = 9.