Show that is increasing on R.
Consider f(x)=x3-15x2+75x-50
Domain of the function is R.
f’(x)=3x2-30x+75
=3(x2-10+25)
=3(x-5) (x-5)
=3(x-5)2
f’(x)=0 for x=5
for x<5
f’(x)>5
and
for x>5
f’(x)>5
we can see throughout R the derivative is +ve but at x=5 it is 0 so it is increasing.