Question

Guided Practice

Find the first, fourth, and eighth terms of the sequence.


an=−2 · 5n−1a subscript n baseline equals negative 2 times 5 superscript n minus 1 baseline


A.
–2; –250; –156,250


B.
0; –250; –156,250


C.
–10; –1000; –10,000,000

Answer 1

A.

–2; –250; –156,250

Explanation:

A(1) = -2 x 5(1) - 1 = -11

A(4) = -2 x 5(4) -1 = -41

A(8) = -2 x 5(8) -1 = -81

...............................................................................................................................................

an=a1(r)^(n-1)

a1=first term

r=common ratio

n=which term

so

an=-2(5)^(n-1)

first term is -2

4th term is subsitue 4 for n

a4=-2(5)^(4-1)

a4=-2(5)^3

a4=-2(125)

a4=-250

4th term is -250

--------------------------

8th term

a8=-2(5)^(8-1)

a8=-2(5)^7

a8=-2(78125)

a8=-156250

8th term is -156250

...............................................................................................................................................

A(1)=2*5^1-1=2*5^0=2*1=2

a(4)=2*5^4-1=2*5^3=2*125=250

a(8)=2*5^8-1=2*5^7=2*78,125=156,250

...............................................................................................................................................

2, 250, 156, 250