WAEC Further Mathematics 2025 Objective — Question 37

Question 37 of 40 from the West African Examinations Council (WAEC) Further Mathematics 2025 Objective paper, with the correct answer and a full explanation.

If M = [[-5,7],[-3,0]], find M⁻¹.

A. [[0,-1/3],[1/7,5/21]]
B. [[0,-1/3],[1/7,-5/21]]Correct
C. [[0,-1/7],[1/3,-5/21]]
D. [[0,-1/3],[-1/7,5/21]]

Explanation

Det(M) = (-5)(0)-7(-3) = 21. M⁻¹ = (1/21)×adjugate = (1/21)[[0,-7],[3,-5]] = [[0,-1/3],[1/7,-5/21]].

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