1. a) (c-9)(c-3)-6c(3c-2)=c²-3c-9c+27-18c²+12c=-17c²+c+27=17c²-c-27
b) 4a(a-5)-(a-10)²=4a²-20a-(a²-20a+100)=4a²-20a-a²+20a-100=3a²-100
c) (b+2)²-12b=b²+4b+4-12b=b²-8b+4=(b-2)²
2. a) 7x³-28x=7x(x²-4)=7x(x-2)(x+2)
b) 5a²-10ab+5b²=5(a²-2ab+b²)=5(a-b)²
c) x³-8=(x-2)(x²+2x+4)