Question 38

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waecmaths question: 

Given that ${{124}_{x}}=7({{14}_{x}})$ find the value of x

Option A: 

12

Option B: 

11

Option C: 

9

Option D: 

8

waecmaths solution: 

\[\begin{align}  & {{124}_{x}}=7({{14}_{x}}) \\ & 1\times {{x}^{2}}+2\times x+4=7(1\times x+4) \\ & {{x}^{2}}+2x+4=7x+28 \\ & {{x}^{2}}-5x-24=0 \\ & (x+3)(x-8)=0 \\ & x=-3\text{ or }x=8 \\\end{align}\]Ignore –3 and accept 8 

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