Number of Integer Solutions

CAT 2022 Slot 2 · Quantitative Ability · Medium · Algebra

The number of integer solutions of the equation (x2−10)(x2−3x−10)=1(x^2 - 10)^{(x^2 - 3x - 10)} = 1 is

Answer

4

Explanation

The equation ab=1a^b = 1 has solutions in three cases: Case 1: b=0b = 0 and a≠0a \neq 0. x2−3x−10=0  ⟹  (x−5)(x+2)=0  ⟹  x=5x^2 - 3x - 10 = 0 \implies (x - 5)(x + 2) = 0 \implies x = 5 or x=−2x = -2. For x=5x = 5: a=25−10=15≠0a = 25 - 10 = 15 \neq 0. For x=−2x = -2: a=4−10=−6≠0a = 4 - 10 = -6 \neq 0. Solutions: x=5,−2x = 5, -2.

Case 2: a=1a = 1. x2−10=1  ⟹  x2=11x^2 - 10 = 1 \implies x^2 = 11, no integer solution.

Case 3: a=−1a = -1 and bb is an even integer. x2−10=−1  ⟹  x2=9  ⟹  x=3x^2 - 10 = -1 \implies x^2 = 9 \implies x = 3 or x=−3x = -3. For x=3x = 3: b=32−3(3)−10=−10b = 3^2 - 3(3) - 10 = -10 (even). For x=−3x = -3: b=(−3)2−3(−3)−10=9+9−10=8b = (-3)^2 - 3(-3) - 10 = 9 + 9 - 10 = 8 (even). Solutions: x=3,−3x = 3, -3.

Total integer solutions = {5,−2,3,−3}\{5, -2, 3, -3\}, which gives 4 solutions.

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