Question 879046
I will do ONE of them and you do the other one based on the method.


Compete the square to put the equation into standard form.
{{{y=-3x^2-21x-18}}}
{{{-3(x^2+7x+6)}}}, missing term to use is {{{(7/2)^2}}}.
{{{-3(x^2+7x+(7/2)^2+6-(7/2)^2)}}}
{{{-3((x+7/2)^2+6-49/4)}}}
{{{-3((x+7/2)^2+24/4-49/4)}}}
{{{y=-3((x+7/2)^2-25/4)}}}
{{{highlight(y=-3(x+7/2)^2+75/4)}}}
The vertex is a maximum, occurring at {{{highlight(75/4)}}}, read directly from the standard form equation.



You can learn more about this in the lesson: 
<a href="http://www.algebra.com/tutors/Completing-the-Square-to-Solve-General-Quadratic-Equation.lesson?content_action=show_dev">http://www.algebra.com/tutors/Completing-the-Square-to-Solve-General-Quadratic-Equation.lesson?content_action=show_dev</a>