Hi, there! I'm happy to help with this.

What is (1/16)^(-1/4)

(A) -1/2

(B) 2

(C) 256^2

(D) 1/2

(E) 4Well, this one combines a few good exponent rules.

First of all:

(any positive number)^(any power at all) = a positive number

so, right away, answer (A) is out.

One BIG idea --- a negative exponent means: take the reciprocal.

a^(-n) = 1/(a^n)

(1/a)^(-n) = a^n

Thus, (1/16)^(-1/4) = 16^(1/4)

Another BIG idea --- a fractional exponent means take a root.

a^(1/2) = the square root of a

a^(1/3) = the cube root of a

a^(1/4) = the fourth root of a

So, 16^(1/4) equals the fourth root of 16. What number, when raised to the fourth power, equals 16? That number is 2, because 2^4 = 2x2x2x2 = 16.

Here's a challenging practice PS on laws of exponents

http://gmat.magoosh.com/questions/725The question at that link should be followed by a complete video solution when you submit your answer.

Does all this make sense? Please let me know if you have any questions.

Mike

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Mike McGarry

Magoosh Test Prep