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IB DP Maths AA SL Study Notes

2.2.1 Basic Transformations

Translations

Translations involve shifting the graph of a function either vertically or horizontally without changing its shape.

  • Vertical Translation: When we add or subtract a constant from a function, it results in a vertical shift of its graph. Specifically, adding a constant c to a function f(x) shifts the graph upwards by c units, while subtracting moves it downwards.
  • Example: The function f(x) = x^2 represents a parabola. If we consider f(x) + 2, the graph will shift upwards by 2 units. On the other hand, f(x) - 3 will move the graph downwards by 3 units. For a deeper understanding of how quadratic functions like these behave, you can refer to the page on quadratic functions.
  • Horizontal Translation: This involves shifting the graph left or right. Replacing x with x - c in a function f(x) results in a rightward shift by c units. Conversely, replacing x with x + c shifts the graph leftward.
  • Example: For the function f(x) = x^2, if we consider f(x - 3), the graph will move 3 units to the right. Similarly, f(x + 4) will shift the graph 4 units to the left. Understanding the domain and range basics can further clarify how these transformations affect a function's output.
IB Maths Tutor Tip: Understanding the order of transformations is crucial. Always apply horizontal shifts before vertical ones when combining transformations to accurately predict and sketch the final graph of a function.

Reflections

Reflections are about flipping the graph of a function over a specific axis.

  • Reflection over the x-axis: When we multiply a function f(x) by -1, it reflects its graph over the x-axis. This transformation results in an inversion of the graph vertically.
  • Example: The function f(x) = x2 is an upward-opening parabola. When we consider -f(x) = -x2, the graph becomes a downward-opening parabola.
  • Reflection over the y-axis: To achieve this, we replace x with -x in a function f(x). The graph then gets mirrored horizontally.
  • Example: The function f(x) = x^3 has a distinct shape, rising to the right and falling to the left. When we consider f(-x), the graph mirrors, falling to the right and rising to the left. To see more about how functions transform, visit the page on basic transformations.

Dilations

Dilations either stretch or compress the graph of a function.

  • Vertical Dilation: By multiplying a function f(x) by a factor a, where a > 1, its graph gets stretched vertically. If 0 < a < 1, the graph compresses vertically. Example: The function f(x) = x^2 represents a parabola. If we consider 2f(x), the graph will stretch vertically. On the other hand, 0.5f(x) will compress the graph. This is similar to the adjustments seen in basics of rational functions, where function behaviour is modified by constants.
  • Horizontal Dilation: This involves compressing or stretching the graph horizontally. Replacing x with x/a, where a > 1, compresses the graph. If 0 < a < 1, the graph stretches.Example: For f(x) = x2, the graph of f(2x) will compress horizontally, while f(0.5x) will stretch it.
IB Tutor Advice: Practise sketching graphs after transformations by starting with simple functions. This helps in visualising complex transformations and improves accuracy in predicting the effects on the graph's shape and position.

Combined Transformations

Functions can undergo multiple transformations simultaneously. When combining transformations, it's essential to apply them in the correct order to achieve the desired result.

Example: Consider the function f(x) = x^2. If we want to shift it 2 units up, reflect it over the x-axis, and stretch it vertically by a factor of 3, the transformed function will be -3f(x) + 2. For further exploration on solving quadratic equations which can arise from such transformations, see the section on solving quadratic equations.

FAQ

Yes, all functions can undergo basic transformations such as translations, reflections, and dilations. However, the resulting graph's behaviour and appearance will depend on the original function's nature. For instance, translating a linear function will still result in a linear function, but its slope and y-intercept might change. Similarly, reflecting a quadratic function over the x-axis will invert its opening direction. It's worth noting that while all functions can be transformed, the meaningfulness or usefulness of the transformation will depend on the context in which the function is being used.

Transformations can impact the periodicity of functions, especially when dealing with trigonometric functions like sine and cosine. Horizontal stretches or compressions will change the period of periodic functions. For instance, if the function f(x) = sin(x) undergoes a horizontal compression by a factor of 2, the resulting function f(2x) = sin(2x) will have half the original period. On the other hand, vertical transformations and reflections don't affect the periodicity but can change the amplitude or invert the function's peaks and troughs. Understanding how transformations affect periodicity is crucial when analysing waveforms, sound signals, and other periodic phenomena.

Understanding basic transformations is foundational in maths because they provide insight into how more complex functions behave. By mastering simple shifts, stretches, and reflections, students can predict how modifications to function equations will affect their graphs. This knowledge becomes especially valuable when dealing with real-world applications where functions might need adjustments to fit specific scenarios. Moreover, many advanced mathematical concepts, like Fourier transforms or eigenfunctions, are rooted in the principles of basic transformations. Hence, a solid grasp of these transformations is crucial for deeper mathematical understanding and application.

The order in which transformations are applied to a function can significantly impact the resulting graph. For instance, if you first reflect a function over the x-axis and then translate it upwards, you'll get a different result than if you first translate it upwards and then reflect. It's essential to follow the order of operations specified, especially when multiple transformations are combined. In general, it's a good practice to apply reflections and dilations before translations. This ensures that the base function's shape is modified before it's moved to its final position on the coordinate plane.

Transformations can either preserve or alter the symmetry of functions. For instance, a horizontal translation won't change the symmetry of a function, but a reflection over the y-axis will turn an odd function into an even function and vice versa. Similarly, vertical reflections (over the x-axis) do not change the even or odd nature of a function. However, vertical stretches or compressions will preserve the symmetry but alter the function's appearance. It's essential to recognise how specific transformations impact symmetry, as this can influence integral calculations, function evaluations, and other mathematical operations.

Practice Questions

Given the function f(x) = x^2, describe the transformation and sketch the graph of the function g(x) = -2f(x - 3) + 1.

The function g(x) = -2f(x - 3) + 1 can be broken down into several transformations of the original function f(x) = x2. Firstly, x - 3 represents a horizontal translation of 3 units to the right. The factor of -2 indicates a vertical stretch by a factor of 2 and a reflection in the x-axis. Lastly, the +1 represents a vertical translation of 1 unit upwards. Therefore, the graph of g(x) is the graph of f(x) which has been reflected in the x-axis, stretched vertically by a factor of 2, translated 3 units to the right, and then 1 unit upwards.

The function h(x) = x^3 undergoes a series of transformations to produce a new function j(x). The graph of j(x) is the graph of h(x) reflected in the y-axis and then translated 2 units downwards. Write down the equation for j(x).

To reflect the function h(x) = x3 in the y-axis, we replace x with -x, giving us h(-x) = (-x)3 = -x3. To then translate this function 2 units downwards, we subtract 2 from the function. Therefore, the equation for j(x) after undergoing the described transformations is j(x) = -x3 - 2.

Dr Rahil Sachak-Patwa avatar
Written by: Dr Rahil Sachak-Patwa
LinkedIn
Oxford University - PhD Mathematics

Rahil spent ten years working as private tutor, teaching students for GCSEs, A-Levels, and university admissions. During his PhD he published papers on modelling infectious disease epidemics and was a tutor to undergraduate and masters students for mathematics courses.

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