20. \( (-2 y)^{5} \)

To simplify \( (-2 y)^{5} \), you first apply the power to both the coefficient and the variable separately. This means you raise -2 to the 5th power, which equals -32, and then raise \( y \) to the 5th power, resulting in \( y^{5} \). So, the expression simplifies to \( -32 y^{5} \). For anyone tackling polynomial expressions, a common mistake is to forget about the negative sign when raising to an odd power. Since the exponent here is 5 (an odd number), the negative stays negative! Always keep an eye on those signs; they can sneak up on you when you least expect it!