(-2×10^4)×(2.5×10^15)÷(-4×10^13)
=[-2×2.5÷(-4)]×(10^4×10^15÷10^13)
=1.25×10^(4+15-13)
=1.25×10^6
-a²x^4y³÷(-5/6)axy²)
=(-1)÷(-5/6)×(a²÷a)×(x^4÷x)×(y³÷y²)
=(6/5)ax³y
(-4a²b³)³÷(-2a³b²)²
=(-4)³×(a²)³×(b³)³÷[(-2)²×(a³)²×(b²)²]
=-64a^6b^9÷(4a^6b^4)
=-64÷4×(a^6÷a^6)×(b^9÷b^4)
=-16b^5