giải phương trình
a) \(\left(5x+2\right)\left(x-7\right)=0\)
b) \(\left(x^2-1\right)\left(x+3\right)=0\)
c) \(x^2-x-6=0\)
d) \(x^2+x-12=0\)
e) \(15\left(x+9\right)\left(x-3\right)\left(x+21\right)=0\)
g) \(\left(x^2+1\right)\left(x^2+4x+4\right)=0\)
i) \(x^4+2x^3-2x^2+2x-3=0\)
h) \(x^2+5x+6=0\)