Answer:
C. The focus is at [tex](-2,-2 \frac{1}{2})[/tex] and the directrix is at [tex]y = -3\frac{1}2.[/tex]
Step-by-step explanation:
First of all, let us learn about the formula to find Focus and Directrix from the standard equation of a parabola.
Standard form of a parabola is given as:
[tex](x - h)^2 = 4p (y - k)[/tex]
where the focus is [tex](h, k + p)[/tex] and
the directrix is [tex]y = k - p[/tex]
Now, we are given the equation of parabola as:
[tex]y= \dfrac{1}2 (x+2)^2 - 3[/tex]
Let us try to convert it to standard form:
[tex]\Rightarrow y+3= \dfrac{1}2 (x+2)^2 \\\Rightarrow 2(y+3)= (x+2)^2 \\\Rightarrow (x+2)^2 = 2(y+3)\\\Rightarrow (x+2)^2 = 4\times \frac{1}{2}(y+3)[/tex]
Comparing the above with standard equation of parabola [tex](x - h)^2 = 4p (y - k)[/tex]:
[tex]h = -2, p = \frac{1}{2}, k = -3[/tex]
So, Focus is at [tex](h, k + p)[/tex]
[tex]k + p = -3+\frac{1}{2} = -2\frac{1}{2}[/tex]
Focus is at [tex](-2, -1\frac{1}2)[/tex].
Equation of directrix:
[tex]y = k - p=-3-\frac{1}{2}\\\Rightarrow y = -3\frac{1}{2}[/tex]
Also, please refer to the attached image for the diagram of given parabola, focus and directrix.
So, the answer is:
C. The focus is at [tex](-2,-2 \frac{1}{2})[/tex] and the directrix is at [tex]y = -3\frac{1}2.[/tex]
