a]
[tex]f(x)=2x+3\\\\2x+3=0\\\\2x=-3 \ \ |:2\\\\x_0=-1,5[/tex]
b]
[tex]f(x)=x^2-9\\\\x^2-9=0\\\\(x+3)(x-3)=0\\\\x_0=-3 \ \vee \ x_0=3[/tex]
