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Laws of Indices Simplified Revision Notes

Revision notes with simplified explanations to understand Laws of Indices quickly and effectively.

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2.1.1 Laws of Indices

Indices

  • An index is a power.
  • Indices is the plural of index.
infoNote

Example:

  • 323^2
  • Index 22

Fraction Indices

  • A fraction index is like a flower:
  • The bottom's the root
  • The top's the power
infoNote

Example:

  • 2723=32=927^{\frac{2}{3}} = 3^2 = 9
  • 1654=25=3216^{\frac{5}{4}} = 2^5 = 32
image

Negative Powers

  • A negative power means 'reciprocal'.
infoNote

Example:

  • 52=251=1255^{-2} = 25^{-1} = \frac{1}{25}
  • Or 52=152=1255^{-2} = \frac{1}{5^2} = \frac{1}{25}
  • (23)3=(32)3=278\left(\frac{2}{3}\right)^{-3} = \left(\frac{3}{2}\right)^3 = \frac{27}{8}
  • Or(23)3=(32)3=3323\left(\frac{2}{3}\right)^{-3} = \left(\frac{3}{2}\right)^3 = \frac{3^3}{2^3}
infoNote

Example:

(0.16)32=(16100)32=(10016)12=(104)3(0.16)^{\frac{3}{2}} = \left(\frac{16}{100}\right)^{-\frac{3}{2}} = \left(\frac{100}{16}\right)^{\frac{1}{2}} = \left(\frac{10}{4}\right)^3

=(52)3=125/8= \left(\frac{5}{2}\right)^3 = 125/8

Basic Index Laws

infoNote

ax×ay=ax+yax÷ay=axy(ax)y=axy \begin{aligned} a^x \times a^y & = a^{x+y} \\ a^x \div a^y & = a^{x-y} \\ (a^x)^y & = a^{xy} \end{aligned}

infoNote

Example:

(4x2y)3×x2y=64x6y3×x2y=64x4y4(4x^2y)^{3} \times x^{-2}y \\= 64x^6y^3 \times x^{-2}y = 64x^4y^4

Practice Questions

infoNote

Q1.

  1. Evaluate (0.2)2(0.2)^{-2}:

(15)2=52=:success[25]\left(\frac{1}{5}\right)^{-2} = 5^2 = :success[25]

  1. Simplify (16a12)34\left(16a^{12}\right)^{\frac{3}{4}}: (16)34=23=8\left(16\right)^{\frac{3}{4}} = 2^3 = 8

:success[8a9] :success[8a^9]

infoNote

Q2.

Find the value of each of the following:

  1. (53)2\left(\frac{5}{3}\right)^{-2}:

(53)2=(35)2=3252=:success[925]\left(\frac{5}{3}\right)^{-2}= \left(\frac{3}{5}\right)^2 = \frac{3^2}{5^2} = :success[\frac{9}{25}]

  1. 813481^{\frac{3}{4}}:

8134=33=:success[27]81^{\frac{3}{4}} = 3^3 = :success[27]

infoNote

Q4.

  1. Evaluate 9129^{-\frac{1}{2}}:

912=31=:success[13]9^{-\frac{1}{2}} = 3^{-1} = :success[\frac{1}{3}]

  1. Simplify (4x4)3y22x2y5\frac{(4x^4)^3 y^2}{2x^2 y^5}:

64x12y22x2y5=:success[32x10y3]\frac{64x^{12} y^2}{2x^2 y^5} = :success[32x^{10} y^{-3}]

infoNote

Summary

  • Multiplying with same base: Add exponents
  • Dividing with same base: Subtract exponents
  • Raising a power to another power: Multiply exponents
  • Product raised to a power: Distribute power to each factor
  • Quotient raised to a power: Apply power to numerator and denominator
  • Zero exponent: Any non-zero base raised to the zero power is :success[1]:success[1]
  • Negative exponent: Reciprocal of the base raised to the positive exponent
  • Fractional exponent: Numerator is the power, denominator is the root
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