point of inflection question

donjt81

Hi guys... I have this problem that i need to verify. I did it but i just want one of you guys to maybe check to see if it is correct.

problem: find the points of inflection on the curve

y = -3x^4 + 4x^3 +36x^2

so first i found y'' = -36x^2 + 24x + 72 = 0
since b^2 - 4ac is not a perfect square i had to use the formula
x = [ -b + sqrt(b^2 - 4ac) ]/2a
and
x = [ -b - sqrt(b^2 - 4ac) ]/2a

by using these i get the values of x as
x = -1.1196
and x = 1.7863

so the points of inflection are (-1.1196, 34.79) and (1.7863, 107.12)

Thanks in advance

alfredbester

Perfect :).