(4.5*10^5)(2*10^3)(3*10^4)
=（4.5×2×3）×10^(5+3+4)
=27×10¹²
=2.7×10¹³
2x^2y(-8y^2)+4x^2y*5y^2
=-16x²y³+20x²y³
=4x²y³
(x+3y)(2x-y)
=2x²+5xy-3y²