3x² + 4 = 0
any help would be excellent thanks
two methods
if you are fimmilar with completing the sqaure
$\displaystyle x^2-5x = (x- \frac{5}{2})^2 - ( \frac{5}{2})^2$
it should be obvious that you will get a minimum when $\displaystyle x- \frac{5}{2} = 0$
can you finish it form there ?
for the second part, if your draw a reasonable sketch of the of the graph it should be obvious.