(4.5×10的5次方)(2×10的3次方)(3×10的4次方) 计算

(4.5×10^5)×(2×10^3)×(3×10^4)
=4.5×2×3×10^5×10^3×10^4
=27×10^12
=2.7×10^13
2x²y×(-8y²)+4x²y×5y²
=-16x²y³+20x²y³
=4x²y³
3x(x²-2x-1)-2x²(x-3)
=3x³-6x²-3x-2x³+6x²
=x³-3x