waec model questions vol1 2023 mathematics

Objective Question 4

Question 4 WAEC_MODEL_QUESTIONS_VOL1 • 2023
Let \(\mathbf{a}=\langle2,-1,3\rangle\) and \(\mathbf{b}=\langle k,4,-2\rangle\). Define \(\mathbf{c}=\mathbf{a}\times\mathbf{b}\). If \(\mathbf{c}\) is perpendicular to the vector \(\mathbf{d}=\langle1,2,k\rangle\), find all possible values of \(k\).
Answer Options
A. -7±√45
B. -7±√49
Correct Answer C. -7±√51
D. -5±√51
Correct Answer
C

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