Advanced Math
Rational Function Reconstruction
See reasoning & distractor design
The student has to reconstruct the function, change representation, solve a new condition and keep track of the final requested expression.
Common traps: stopping after finding a and b; sign errors in the rewrite; finding x but forgetting c + d.
From (0, −3), b = 12. From (2, −5), a = −1. So f(x) = (−x + 12)/(x − 4) = −1 + 8/(x − 4). Thus c = −1 and d = 8. Solving f(x) = 7 gives x = 5, so x + c + d = 12.