Answer:
Explanation:
fifteen
14 8 2 -4 - 10 ,,,,,
This series is arithmetic. Each term has 6 less than the preceding one.
Sixteen
16 is geometric. Multiply the previous term by 4 to get the next one. 12*4 =48
Seventeen Not there
Eighteen
14, 8, 2, -4 , - .....
a = 14
d = - 6
n = 68
L= a + (n - 1)*-6
L = 14 + (68 - 1) * - 6
This then becomes a calculator problem. I can't turn a light on to read this.
Nineteen
a7 = a1 + (7-1)*d
9 = a1 + 7d - d
9 = a1 + 6n .... Equation one
21 = a1 + (d-1 )21
21 = a1 + 21d - 21
42 = a1 + 21d ...... Equation two. They can combine. You'll have to solve for d first and then a1