The way others have noted is "using Vieta's Equations in reverse," if you'd like to look into it. I try to avoid the memorization required.
Alternatively, we can assign values to constants and solve through.
A = 4
B = 16
C = -9
These can be any value, but I think making A anything besides +1/-1/0 makes it easier to understand.
Note* During a test, these can be adjusted if the original numbers you choose can't be easily factored.*
Therefore Equation one = 4x^2 + 16x - 9 = 0
Factor using the box method
(2x+9)(2x-1) = 0
Roots after solving = x = -9/2 , 1/2
the reciprocals of these are -2/9 and 2 which can be translated into: (9x+2)(-x+2) = 0
Foil that back out =.
-9x^2 + 18x - 2x +4
-9x^2 + 16x +4 =0
Replace assigned variables
4 = A
16 = B
-9 = C
Cx^2 + Bx + A = 0
Answer = A
Bunuel
What is the equation whose roots are reciprocals of the roots of \(ax^2 + bx + c = 0\)?
A. \(cx^2 + bx + a = 0\)
B. \(cx^2 - bx + a = 0\)
C. \(cx^2 + bx - a = 0\)
D. \(cx^2 - bx - a = 0\)
E. \(cx^2 + bx + a^2 = 0\)