Let f(x)=(x-1)(3x-4)f(x)=(x−1)(3x−4)
Let's do the sign chart
color(white)(aaaa)aaaaxxcolor(white)(aaaa)aaaa-oo−∞color(white)(aaaa)aaaa11color(white)(aaaa)aaaa4/343color(white)(aaaa)aaaa+oo+∞
color(white)(aaaa)aaaax-1x−1color(white)(aaaa)aaaa-−color(white)(aaaa)aaaa++color(white)(aaaa)aaaa++
color(white)(aaaa)aaaa3x-43x−4color(white)(aaaa)aaaa-−color(white)(aaa)aaa-−color(white)(aaaa)aaaa++
color(white)(aaaa)aaaaf(x)f(x)color(white)(aaaaaa)aaaaaa++color(white)(aaaa)aaaa-−color(white)(aaaa)aaaa++
So, f(x)>=0f(x)≥0 for x in ] -oo,1 ] uu [ 4/3, +oo[ x∈]−∞,1]∪[43,+∞[
graph{y=(x-1)(3x-4) [-1.863, 3.006, -1.232, 1.2]}