Functions & Algebra

Transformations of Exponential, Logarithmic, and Trigonometric Functions

Grade 10 · Grade 11 · Grade 12

  • ✓By the end of this lesson students will be able to describe the effects of transformations (stretches, compressions, reflections, translations) on exponential, logarithmic, and trigonometric functions.
  • ✓By the end of this lesson students will be able to apply transformations to graph exponential, logarithmic, and trigonometric functions.
  • ✓By the end of this lesson students will be able to determine the equation of a transformed exponential, logarithmic, or trigonometric function given its graph or a description of the transformations.
  • ✓By the end of this lesson students will be able to solve problems involving transformations of these function types.
  • ✓By the end of this lesson students will be able to utilize properties of logarithms to simplify expressions and solve equations.

Key concepts

General Transformations of Functions

Any function y = f(x) can be transformed into the form y = af(k(x-d)) + c. Each parameter affects the graph in a specific way:\n- 'a': Vertical stretch or compression by a factor of |a|. If a < 0, there is a reflection across the x-axis.\n- 'k': Horizontal stretch or compression by a factor of 1/|k|. If k < 0, there is a reflection across the y-axis.\n- 'd': Horizontal translation (phase shift). The graph shifts 'd' units to the right if d > 0, and 'd' units to the left if d < 0.\n- 'c': Vertical translation. The graph shifts 'c' units up if c > 0, and 'c' units down if c < 0.\n\nThe order of applying transformations is crucial: stretches, compressions, and reflections are applied first, followed by translations.

y = af(k(x-d)) + c
Transformations of Exponential Functions

An exponential function in its base form is y = b^x, where b > 0 and b ≠ 1. The transformed form is y = a * b^(k(x-d)) + c.\n- The horizontal asymptote of the base function y = b^x is y = 0. For the transformed function, the horizontal asymptote is y = c.\n- The domain is always x ∈ R.\n- The range is y > c if a > 0, and y < c if a < 0.

y = a * b^(k(x-d)) + c
Transformations of Logarithmic Functions

A logarithmic function in its base form is y = log_b(x), where b > 0 and b ≠ 1. This is the inverse of y = b^x. The transformed form is y = a * log_b(k(x-d)) + c.\n- The vertical asymptote of the base function y = log_b(x) is x = 0. For the transformed function, the vertical asymptote is x = d.\n- The domain is x > d if k > 0, and x < d if k < 0.\n- The range is always y ∈ R.

y = a * log_b(k(x-d)) + c
Properties of Logarithms

Logarithms follow specific rules that are essential for simplifying expressions and solving equations:\n- Product Rule: The logarithm of a product is the sum of the logarithms.\n- Quotient Rule: The logarithm of a quotient is the difference of the logarithms.\n- Power Rule: The logarithm of a power is the exponent times the logarithm of the base.\n- Change of Base Formula: Allows conversion between different logarithm bases.

log_b(MN) = log_b(M) + log_b(N)\nlog_b(M/N) = log_b(M) - log_b(N)\nlog_b(M^p) = p * log_b(M)\nlog_b(x) = log_c(x) / log_c(b)
Transformations of Trigonometric Functions

The base forms are y = sin(x) and y = cos(x). The transformed form is y = a * sin(k(x-d)) + c or y = a * cos(k(x-d)) + c.\n- 'a': Amplitude = |a|. This is half the distance between the maximum and minimum values. If a < 0, there is a reflection across the x-axis.\n- 'k': Determines the period. Period = (2π / |k|) for radians or (360° / |k|) for degrees. If k < 0, there is a reflection across the y-axis.\n- 'd': Phase shift. Horizontal translation. 'd' units right if d > 0, 'd' units left if d < 0.\n- 'c': Vertical shift. The equation of the axis of the curve is y = c.\n- Maximum value = c + |a|, Minimum value = c - |a|.

y = a * sin(k(x-d)) + c\ny = a * cos(k(x-d)) + c

Key facts to remember

  • 1The general transformation form for any function f(x) is y = af(k(x-d)) + c.
  • 2For exponential functions y = a * b^(k(x-d)) + c, the horizontal asymptote is y = c.
  • 3For logarithmic functions y = a * log_b(k(x-d)) + c, the vertical asymptote is x = d.
  • 4The period of y = a sin(k(x-d)) + c or y = a cos(k(x-d)) + c is 2π/|k| (for radians) or 360°/|k| (for degrees).
  • 5The amplitude of a sinusoidal function is |a|, and the equation of the axis is y = c.
  • 6Key logarithm properties: log_b(MN) = log_b(M) + log_b(N), log_b(M/N) = log_b(M) - log_b(N), log_b(M^p) = p log_b(M).
  • 7Special logarithm values: log_b(b) = 1 and log_b(1) = 0.

Worked examples

Example 1

Describe the transformations applied to the base function y = 2^x to obtain y = -3 * 2^(0.5(x+4)) - 1. State the equation of the asymptote.

IIdentify the parameters a, k, d, and c from the transformed function y = -3 * 2^(0.5(x+4)) - 1.
IIHere, a = -3, k = 0.5, d = -4, c = -1.
IIIDescribe the effect of 'a': a = -3 means a vertical stretch by a factor of 3 and a reflection across the x-axis.
IVDescribe the effect of 'k': k = 0.5 means a horizontal stretch by a factor of 1/0.5 = 2.
VDescribe the effect of 'd': d = -4 means a horizontal translation 4 units to the left.
VIDescribe the effect of 'c': c = -1 means a vertical translation 1 unit down.
VIIThe horizontal asymptote for the base function y = 2^x is y = 0. For the transformed function, the asymptote is y = c.
VIIITherefore, the equation of the asymptote is y = -1.

Answer

The transformations are: a vertical stretch by a factor of 3, a reflection across the x-axis, a horizontal stretch by a factor of 2, a horizontal translation 4 units left, and a vertical translation 1 unit down. The equation of the asymptote is y = -1.

Remember to factor out 'k' if it's not already factored, e.g., y = 2^(2x+4) should be written as y = 2^(2(x+2)).

Example 2

Simplify the logarithmic expression: log_3(27x^5) - log_3(9x^2).

IApply the Quotient Rule of logarithms: log_b(M) - log_b(N) = log_b(M/N).
IIlog_3(27x^5) - log_3(9x^2) = log_3((27x^5) / (9x^2))
IIISimplify the expression inside the logarithm.
IVlog_3(3x^3)
VApply the Product Rule of logarithms: log_b(MN) = log_b(M) + log_b(N).
VIlog_3(3) + log_3(x^3)
VIIApply the Power Rule of logarithms: log_b(M^p) = p * log_b(M).
VIIIlog_3(3) + 3 * log_3(x)
9Evaluate log_3(3). Since log_b(b) = 1, log_3(3) = 1.
101 + 3 * log_3(x)

Answer

1 + 3log_3(x)

Ensure x > 0 for the logarithm to be defined.

Example 3

A sinusoidal function has an amplitude of 4, a period of π, a phase shift of π/6 to the right, and a vertical shift 3 units up. Write the equation of this function using a sine function.

IIdentify the amplitude 'a'. Amplitude = 4, so |a| = 4. We can choose a = 4.
IIIdentify the period. Period = π. Use the formula Period = 2π / |k| to find 'k'.
IIIπ = 2π / |k| => |k| = 2. We can choose k = 2.
IVIdentify the phase shift 'd'. Phase shift π/6 to the right means d = π/6.
VIdentify the vertical shift 'c'. Vertical shift 3 units up means c = 3.
VISubstitute these values into the general sine equation y = a * sin(k(x-d)) + c.
VIIy = 4 * sin(2(x - π/6)) + 3

Answer

y = 4sin(2(x - π/6)) + 3

If the problem asked for a cosine function, the phase shift 'd' would be different for the same graph.

Common mistakes

  • ✗Incorrectly applying the order of transformations: stretches/compressions/reflections must be applied before translations.
  • ✗Misinterpreting the 'k' value: a horizontal stretch/compression is by a factor of 1/|k|, not |k|.
  • ✗Errors with the sign of 'd': (x+d) means a shift left by 'd' units (d is negative in the general form x-d).
  • ✗Applying logarithm properties incorrectly, such as assuming log(M+N) = log M + log N.
  • ✗Forgetting to factor 'k' out of the x-term in trigonometric functions, leading to an incorrect phase shift (e.g., sin(2x + π/2) should be sin(2(x + π/4))).
  • ✗Not stating the domain and range or asymptotes for transformed functions.

Exam tips

  • ★Always factor 'k' out of the x-term in the argument of the function to correctly identify the horizontal stretch/compression and phase shift.
  • ★Sketch the base function first, then apply transformations one by one (stretches/reflections, then translations) to key points to accurately graph the transformed function.
  • ★For trigonometric functions, pay close attention to whether angles are in degrees or radians, as this affects the period calculation.
  • ★Review and memorize all logarithm properties and be ready to apply them to simplify expressions or solve equations.

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