A sequence is formed by multiplying each term by the same integer and begins 1, -2, 4, -8. Which term comes next?

Explication

Every term is the one before it multiplied by two below zero, so multiplying eight below zero by that factor reverses the sign once more and doubles the size, reaching sixteen above zero. Keeping the result below zero ignores that the signs alternate, and treating the pattern as a repeated addition misses the doubling entirely.