Number System & Expressions/Equations

Exponents, Scientific Notation, and Irrational Numbers

Grade 8

  • ✓By the end of this lesson students will be able to apply the properties of integer exponents to simplify expressions.
  • ✓By the end of this lesson students will be able to convert numbers between standard form and scientific notation.
  • ✓By the end of this lesson students will be able to perform operations (multiplication, division, addition, subtraction) with numbers expressed in scientific notation.
  • ✓By the end of this lesson students will be able to define and identify irrational numbers, distinguishing them from rational numbers.
  • ✓By the end of this lesson students will be able to approximate irrational numbers by using rational numbers.

Key concepts

Integer Exponents

An exponent tells us how many times a base number is multiplied by itself. For example, in 'a^n', 'a' is the base and 'n' is the exponent. Integer exponents include positive whole numbers, zero, and negative whole numbers. Understanding the properties of exponents allows us to simplify expressions efficiently.\n\nProperties of Integer Exponents:\n1. Product of Powers: When multiplying powers with the same base, add the exponents.\n2. Quotient of Powers: When dividing powers with the same base, subtract the exponents.\n3. Power of a Power: When raising a power to another power, multiply the exponents.\n4. Power of a Product: To raise a product to a power, raise each factor to the power.\n5. Power of a Quotient: To raise a quotient to a power, raise both the numerator and the denominator to the power.\n6. Zero Exponent: Any non-zero base raised to the power of zero is 1.\n7. Negative Exponent: A negative exponent indicates the reciprocal of the base raised to the positive exponent.

a^n · a^m = a^(n+m)\na^n / a^m = a^(n-m)\n(a^n)^m = a^(n·m)\n(ab)^n = a^n b^n\n(a/b)^n = a^n / b^n\na^0 = 1 (where a ≠ 0)\na^(-n) = 1/a^n (where a ≠ 0)
Scientific Notation

Scientific notation is a way to write very large or very small numbers concisely. It is expressed as a product of two factors: a coefficient and a power of 10. The coefficient must be a number greater than or equal to 1 and less than 10 (1 ≤ M < 10). The power of 10 indicates how many places the decimal point was moved and in which direction (positive for large numbers, negative for small numbers).

M × 10^n, where 1 ≤ M < 10 and n is an integer.
Operations with Scientific Notation

Performing operations with numbers in scientific notation involves applying exponent rules and careful handling of the coefficients.\n\nMultiplication: Multiply the coefficients and add the exponents of 10.\nDivision: Divide the coefficients and subtract the exponents of 10.\nAddition/Subtraction: Adjust the numbers so they have the same power of 10, then add or subtract the coefficients. The power of 10 remains the same. After any operation, ensure the result is in proper scientific notation (1 ≤ M < 10).

Irrational Numbers

Rational numbers are numbers that can be expressed as a fraction p/q, where p and q are integers and q is not zero. Their decimal representations either terminate (e.g., 0.5) or repeat (e.g., 0.333...). \n\nIrrational numbers are numbers that cannot be expressed as a simple fraction p/q. Their decimal representations are non-terminating AND non-repeating. Famous examples include pi (π) and the square root of any non-perfect square (e.g., √2, √7).

Approximating Irrational Numbers

Since irrational numbers have non-terminating, non-repeating decimals, we often need to approximate their values. For square roots, we can estimate by finding the two consecutive perfect squares that the number under the radical falls between. This helps us place the irrational number on a number line between two integers or estimate its decimal value.

Key facts to remember

  • 1Any non-zero number raised to the power of zero is 1 (e.g., 5^0 = 1).
  • 2A negative exponent means to take the reciprocal of the base raised to the positive exponent (e.g., x^-n = 1/x^n).
  • 3In scientific notation (M × 10^n), the coefficient M must satisfy 1 ≤ M < 10.
  • 4To multiply numbers in scientific notation, multiply the coefficients and add the exponents of 10.
  • 5To divide numbers in scientific notation, divide the coefficients and subtract the exponents of 10.
  • 6Irrational numbers have decimal representations that are non-terminating and non-repeating.
  • 7Rational numbers can be written as a fraction p/q, and their decimals either terminate or repeat.
  • 8To approximate an irrational square root, find the two consecutive perfect squares it lies between.

Worked examples

Example 1

Simplify the expression: (4x^3y^-2)^2 · (2x^-1y^5)

IApply the Power of a Product rule to the first term: (4x^3y^-2)^2 = 4^2 · (x^3)^2 · (y^-2)^2
IIApply the Power of a Power rule: 16 · x^(3·2) · y^(-2·2) = 16x^6y^-4
IIINow multiply this result by the second term: (16x^6y^-4) · (2x^-1y^5)
IVGroup like bases: (16 · 2) · (x^6 · x^-1) · (y^-4 · y^5)
VApply the Product of Powers rule: 32 · x^(6 + (-1)) · y^(-4 + 5)
VISimplify the exponents: 32 · x^5 · y^1
VIIWrite the final simplified expression.

Answer

32x^5y

Remember to apply the exponent rules carefully, especially when dealing with negative exponents and powers of products.

Example 2

Calculate (6.3 × 10^8) ÷ (2.1 × 10^3) and express the answer in scientific notation.

ISeparate the coefficients and the powers of 10: (6.3 ÷ 2.1) × (10^8 ÷ 10^3)
IIDivide the coefficients: 6.3 ÷ 2.1 = 3
IIIApply the Quotient of Powers rule for the powers of 10: 10^8 ÷ 10^3 = 10^(8-3) = 10^5
IVCombine the results: 3 × 10^5
VCheck if the coefficient is between 1 and 10. In this case, 3 is between 1 and 10, so no further adjustment is needed.

Answer

3 × 10^5

If the coefficient had been, for example, 30, you would need to rewrite it as 3.0 × 10^1 and then adjust the power of 10 accordingly (3.0 × 10^1 × 10^5 = 3.0 × 10^6).

Example 3

Between which two consecutive integers does √50 lie? Explain your reasoning.

IIdentify the number under the radical: 50.
IIFind the perfect squares closest to 50, one less than 50 and one greater than 50.
IIIThe perfect square less than 50 is 49 (since 7^2 = 49).
IVThe perfect square greater than 50 is 64 (since 8^2 = 64).
VSince 49 < 50 < 64, it follows that √49 < √50 < √64.
VISimplify the square roots of the perfect squares: 7 < √50 < 8.
VIIState the conclusion based on the inequality.

Answer

√50 lies between the integers 7 and 8. This is because 7^2 = 49 and 8^2 = 64, and 50 is between 49 and 64.

This method helps to approximate the value of irrational square roots without using a calculator, by placing them between known rational numbers.

Common mistakes

  • ✗Forgetting that a^0 = 1, not 0.
  • ✗Confusing negative exponents with negative numbers (e.g., 2^-3 is not -8, it's 1/8).
  • ✗Incorrectly adjusting the exponent when converting to or from scientific notation, especially when the coefficient is not between 1 and 10.
  • ✗Adding or subtracting numbers in scientific notation without first making sure they have the same power of 10.
  • ✗Mistaking repeating decimals for irrational numbers; repeating decimals are rational.

Exam tips

  • ★Always show your steps when simplifying exponent expressions; partial credit can be awarded for correct application of rules.
  • ★Double-check that your final answer in scientific notation has a coefficient (M) such that 1 ≤ M < 10.
  • ★When approximating irrational numbers, clearly state the perfect squares you are using for your estimation.
  • ★Practice distinguishing between rational and irrational numbers by considering their decimal forms or whether they can be written as a fraction.

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