The reflecting dish of a parabolic microphone has a cross-section in the shape of a parabola. The microphone itself is placed on the focus of the parabola. If the parabola is 24 inches wide and 4 inches deep, how far from the vertex should the microphone be placed? (1 point)


4 inches


18 inches


9 inches


12 inches

Verified Answer :

we are given a microphone that has a shape of a parabola in which the dimensions are 24 inches wide and 4 inches deep. In this case, we can put the vertex at the origin, that is Place the vertex at the origin. Then the parabola has equation 
4ay = x² 
4a(4) = 12^2 
a = 9 in 
THe answer then is C.

Answer: 9 inches.


Step-by-step explanation:

Given: The width of the parabola= 24 inches

The depth of the parabola = 4 inches

Assume the parabola open upwards and the vertex of the parabola be (0,0)

Then the point on parabola (x,y)=\((-\frac{24}{2},4)\ and (+\frac{24}{2},4)\)

⇒ (-12,4) and (12,4) are points on parabola.

Equation of parabola opens upwards with vertex=(0,0) is \(x^2=4ay\)

Put (12,4) in the equation, we get

\((12)^2=4a(4)\\\Rightarrow\ 144=16a\\\Rightarrow\ a=\frac{144}{16}=9\\\Rightarrow\ a=9\)

Since, the microphone itself is placed on the focus of the parabola.

Hence, the microphone is 9 inches far from the vertex.