[tex]10a^2bc^4-15b^2c^3=5(2a^2bc^4-3b^2c^3)=5b(2a^2c^4-3bc^3)=5bc^3(2a^2c-3b)[/tex]

[tex]\dfrac{-x^2+y^2-2xy}{-x^3-y^5}\\\\\dfrac{-3^2+(-2)^2-2\cdot3\cdot(-2)}{-3^3-(-2)^5}=\dfrac{-9+4-(-12)}{-27-(-32)}=\dfrac{-5+12}{-27+32}=\dfrac{7}{5}[/tex]