Question

What is the equation of the directrix of the parabola defined by the equation shown below? h v2 = - 36x O A. x = 4 O B. y = 9 O C. x= 9 O D. y = -6 SUBMIT E PREVIOUS Type here to search o

Answer 1

The correct option is:

C. x = 9

To find the directrix, we need to write the parabolla in the form:

$y^2=4ax$

Then, we have a (-36) that we want to write as 4 times a numer "a".

$\begin{gathered} -36=4\cdot a \\ -\frac{36}{4}=a \\ -9=a \end{gathered}$

The parabolla is:

$y^2=4(-9)x$

The directrix line is simply x = -a

In this case a = -9 then -a = 9

The directrix is x = 9