Let's factorise the expression,
x^2+x-6=(x-2)(x+3)x2+x−6=(x−2)(x+3)
and let f(x)=x^2+x-6f(x)=x2+x−6
Now we can do the sign chart
color(white)(aaaa)aaaaxxcolor(white)(aaaa)aaaa-oo−∞color(white)(aaaa)aaaa-3−3color(white)(aaaaa)aaaaa22color(white)(aaaa)aaaa+oo+∞
color(white)(aaaa)aaaax+3x+3color(white)(aaaaa)aaaaa-−color(white)(aaaa)aaaa++color(white)(aaaa)aaaa++
color(white)(aaaa)aaaax-2x−2color(white)(aaaaa)aaaaa-−color(white)(aaaa)aaaa-−color(white)(aaaa)aaaa++
color(white)(aaaa)aaaaf(x)f(x)color(white)(aaaaaa)aaaaaa++color(white)(aaaa)aaaa-−color(white)(aaaa)aaaa++
Therefore,
f(x)<0f(x)<0, when x in ] -3,2 [ x∈]−3,2[