<span>x^2 + 8x = -3
</span><span>x^2 + 8x + 16 = -3 + 16
using a^2 + 2 a b + b^2 = (a+b)^2
</span><span>
</span>x^2 + 8x + 16 = 13
<span>(x +4)^2 = 13
answer : 16 is the number </span><span>you must add to complete the square</span>
Answer:

it seems like the first term is -64, so lets write the formula accordingly:
a_n = a1(r)^(n-1)
where 'n' is the number of terms
a1 is the first term of the sequence
'r' is the ratio
the ratio is
because -64 *
= 16 and so on...
the explicit formula is :
= 
Sorry about the bad handwriting
I uploaded the answer to a file hosting. Here's link:
tinyurl.com/wpazsebu