（20a³-5a²b²×3a²b)÷(-5a³b²)
=(20a³-15a^4·b³)÷(-5a³b²)
=-4b^(-2)+3ab²
x=-1
(x-3)²+(x-2)(-2-x)
=(x-3)²-(x-2)(x+2)
=x²-6x+9-x²+4
=-6x+13
=6+13
=19