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Reason:
[tex]2^6[/tex] means we have 6 copies of "2" multiplied out as shown in choice B. That explains how A and B are the same, and we can say
[tex]2^6 = (2*2*2)*(2*2*2)[/tex]
The parenthesis are optional, but I find they're handy to count the '2's easier.
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Now notice that
[tex]2^3 = 2*2*2[/tex]
So,
[tex]2^6 = (2*2*2)*(2*2*2)\\\\2^6 = (2^3)*(2^3)\\\\2^6 = (2^3)^2\\\\[/tex]
The last step is possible because we have two copies of [tex]2^3[/tex] multiplied together.
This shows that choice C is equivalent to A and B.
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Lastly,
[tex]2^6 = (2*2*2)*(2*2*2)\\\\2^6 = (2*2)*(2*2)*(2*2)\\\\2^6 = (2^2)*(2^2)*(2^2)\\\\2^6 = (2^2)^3\\\\[/tex]
The jump to the last step is possible because we have three copies of [tex]2^2[/tex] multiplied together.
This shows choice D is equivalent to the others.
All four expressions are the same.
They represent different ways to say the same number. That number being 64.