-4u^5(-u^5)

Expanding the expression, we have:

-4u^5(-u^5) = -4u^5 * -u^5

Since we have a negative times a negative, it results in a positive:

-4u^5 * -u^5 = 4u^5 * u^5

Multiplying the coefficients, we get:

4 * 1 = 4

Multiplying the variables, we add the exponents:

u^5 * u^5 = u^(5+5) = u^10

Therefore, the simplified expression is:

-4u^5(-u^5) = 4u^10