Question

Help me please, this stuff is difficult.

If 1 = 10 a 1 ​ =10 and = − 2 − 1 a n ​ =−2a n−1 ​ then find the value of 4 a 4 ​ .

Answer 1

Answer: -80

Step-by-step explanation:

a1 = 10

a2 = -2 x 10 = -20

a3 = -2 x -20 = 40

a4 = -2 x 40 = -80

Answer 2

an = -2an - 1 - n

Let's find a2 (so make n = 2):

a2 = -2(a2-1) - 2 = -2(a1) - 2 = -2(4) - 2 = -8 - 2 = -10

Now let's find a3 (so make n = 3):

a3 = -2(a3-1) - 3 = -2(a2) - 3 = -2(-10) - 3 = 20 - 3 = 17

Now let's find a4 (so make n = 4):

a4 = -2(a4-1) - 4 = -2(a3) - 4 = -2(17) - 4 = -34 - 4 = -38

Now let's find a5 (so make n = 5):

a5 = -2(a5-1) - 5 = -2(a4) - 5 = -2(-38) - 5 = 76 - 5 = 71