1) 3a³-12ab²=3a(a²-4b²)=3a(a²-(2b)²)=3a(a-2b)(a+2b)
2) (-2x³y)²(3xy²)=(-2)² * (x³)² * y² * 3x * y²=4* x⁶ * y² *3x *y²=12x⁶⁺¹y²⁺²=12x⁷y⁴
3) (2x-7)(x+1)=0
2x²+2x-7x-7=0
2x²-5x-7=0
D=5²+4*7*2=25+56=81=9²
x₁=(5+9)/4=14/4=3.5
x₂=(5-9)/4=-4/4=-1
4)4x²-9=0
4x²=9
x²=9/4
x₁=+√(9/4)=3/2
x₂=-√(9/4)=-3/2