Work Step by Step
Let us solve the given problem in the following way: $a^2-a-12=0$ or, $a^2-4a+3a-12=0$ or, $(a+3)(a-4)=0$ This can be written as : $a+3=0$ or, $a-4=0$ Thus, $a=-3,4$ Hence, the final answer will be $(d)$.
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