The principle of powers and roots is an integral part of many concepts and topics in mathematics. A thorough understanding of power and roots is essential for learning complex mathematical topics like trigonometry, calculus, polynomials, graphs, etc.

Power

A power or an index is a representation of the repeated multiplication of a certain number. Powers are denoted in the form of an where ‘a’ is the base number and ‘n’ is the power it possesses.

For example, 23 = 2x2x2 and 34 = 3x3x3x3.

It enables us to break a large number into small fragments of prime numbers and their powers. For example, 7056 = 24x33x72 and 1125 = 32x53

A negative power in a number indicates that it divides the other components in that fraction. For example, 2-2=\frac{1}{2*2}=\frac{1}{4} and 32x 42x 5-2= \frac{3*3*4*4}{5*5}= \frac{144}{25}

*NOTE: 0 with negative power is not defined.

Properties of Power

Let’s understand the properties of indices with examples.

1. a0Any non-zero number possessing 0 as power is 1.

a0 = 1. For example, 20= 1 and 50= 1

*NOTE: 00 is not defined.

1. a1Any number comprising 1 as its power is itself.

a1= a. For example, 61= 6 and 111= 11

1. 0n0 with a certain power can be defined as

0n if n>0 = 0. For example, 09= 0 and 07= 0

0n if n<0 = not defined.

1. 1n1 to the power of any integer is 1.

1n= 1. For example, 123= 1 and 1-23= 1

1. (-a)nPowers of negative integers can be explained as

(-a)n , if n is even, will give a positive number. For example, (-2)4= 16 and (-5)-2= 125.

(-a)n, if n is odd, will give a negative number. For example, (-7)3= -343 and (-11)-1= -111.

Mathematical Operations of Powers

To simplify the equations with numbers containing powers, various mathematical tools are used.

• Entities with the same powers

anx bn= (ab)n. For example, 22x32= (2×3)2= 62= 36.

an/bn= abn. For example, 52/72= 572= 2549.

• Entities with the same base

anx am= (a)n+m. For example, 32x33= (3)2+3= (3)5= 243

an/am= (a)n-m. For example. 53/52= (5)3-2= (5)1= 5

(an)m= anm. For example, (22)3= 22×3= 26= 64.

Roots

The usage of roots is the inverse operation of powers. Roots are denoted by \sqrt[n]{a} where ‘a’ is the base number and ‘n’ denotes the repeated multiplication a certain number goes through to become ‘a’.

For example, 23= 8 and \sqrt{8} = 2.

Square Roots and Cube Roots

A root in the form of \sqrt[n]{a} where n = 2 is called a square root and a root in the form of \sqrt[n]{a}  where n = 3 is called a cube root. Generally, square roots are showcased without mentioning the ‘n’ component of the root form, i.e, \sqrt{8}

For example,   \sqrt{49} = 7 and \sqrt{121} = 11.

These are the most common roots that are used across different disciplines of mathematics.

Properties of Roots

Following are the properties that regulate the functions of roots.

1. \sqrt[n]{a} x \sqrt[n]{b} = \sqrt[n]{ab} . For example, \sqrt{1331}x \sqrt{343} = \sqrt{1331*343}= 11×7 = 77.
2.  nanb = \sqrt[n]{\frac{a}{b}} . For example, 481416 = \sqrt{\frac{81}{16}} = \frac{3}{2} = 1.5
3. a^{\frac{1}{n}} = \sqrt[n]{a} . For example, 412 = \sqrt{4} = 2.
4. \sqrt[n]{a}+\sqrt[n]{b} \sqrt[n]{a+b} . For example, \sqrt{27}+\sqrt{125} because \sqrt{27} = 3 and \sqrt{125} = 5 and 3+5 = 8, but \sqrt{27+125} i.e \sqrt{152} \neq 8.

*NOTE: negative roots (complex numbers) are not included in the syllabus of GMAT.

Sample Question

If 0<m<1, then which of the following must be true?

1. _{m}2>\frac{1}{m}> \sqrt{m}
2. \frac{1}{m}​> _{m}2 > \sqrt{m}
3. \frac{1}{m}​> \sqrt{m} > _{m}2
4. \sqrt{m} > _{m}2 > \frac{1}{m}
5. \sqrt{m} > \frac{1}{m}​> _{m}2

Explanation:

Plug in the value for m and check the answer options.

m=\frac{1}{2}

then

_{m}2=\frac{1}{4}=0.25 , \sqrt{m}=\frac{1}{\sqrt{6}}≈0.7  and \frac{1}{m}=\frac{1}{\frac{1}{2}}=2

So, then the correct ordering from greatest to least is \frac{1}{m}​ > \sqrt{6} > _{m}2