(x+1)(x-4) is greater than or equal to (x-2)^2
(x+1)(x-4) >= (x-2)^2
x^2-3x-4 >= x^2-4x+4
x >= 8
for the graphs, go to wolframalpha.com and enter
plot y=(x+1)(x-4) , y=(x-2)^2, x=6..10
or, enter
(x+1)(x-4)-(x-2)^2
and see where it's positive