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If the two identical solid cubes of side x are joined end to end, then the total surface area of the resulting cuboid is 12x^{2}. Is it true?

= 2 { 2x*x + x*x + 2x*x}

= 2 { 2x^2 + x^2 + 2x^2}

= 2 { 5x^2}

= 10x^2

but, 10x^2 is not equal to 12x^2 ,

therefore, it is false

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