Problem: if a 2 - b 2 = 9 and a * b = 4 , find a 4 + b 4 .
Rationale: "a 2 - b 2 = 9 : given a 4 + b 4 - 2 a 2 b 2 = 92 : square both sides and expand . a * b = 4 : given a 2 b 2 = 42 : square both sides . a 4 + b 4 - 2 ( 16 ) = 81 : substitute a 4 + b 4 = 113 correct answer c"
annotated_formula: add(power(9, 2), multiply(power(4, 2), 2))