Minimum value of quadratic equation I know that $ax^2+bx+c$ if $a &lt; 0$ it has maximum value and we find $m = -b/2a$
but if $a&gt;0$ it should have minimum value how can find it?
Thanks in advance.
It's the same $m = \frac{-b}{2a}$. One way you can notice this is as follows: Suppose the 2nd degree polynomial $ax^2+bx+c$ has $a&gt;0$. Then multiply through by $-1$ and you'll have a 2nd degree polynomial with $a&lt;0$. As you pointed out, the second polynomial will have minimum at $x = \frac{-b}{2a}$. This must mean the same value of $x$ gives a maximum in the first polynomial.
It is very simple.

If $a&lt;0$ implies that $ax^2+bx+c$ has a maximum, then $-ax^2-bx-c$ (such that $-a&gt;0$) has a minimum, and these two functions are mirrors of each other around the horizontal axis.