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Functions, relations and inverses
Definition: A relation is when a variable gets related to another variable by use of any formulae or
equation, ie x gets related to y. How y reacts to x gives us the different graphs.
A function is a special relation for which each x only has one y. The moment that that is
not the case, we have a non-function.
There are 9 different graphs you have to be able to analyse, interpret and sketch:
• Straight line
• Parabola
• Cubic
• Hyperbola
• Exponential
• Logarithmic
• Sine
• Cosine
• Tangent
There are certain questions, which you must be able to answer for all 9 graphs:
1. 𝒙-intercept:
o Let 𝑦 = 0.
2. y-intercept:
o Let 𝑥 = 0.
3. Definition/Domain:
o All 𝑥-values for which the function is defined.
4. Rang
o All y-values for which the function is defined.
5. Intersection between graphs:
o Set the y-values equal to each other or
o Use substitution to solve simultaneously.
6. Inverse relations:
o An inverse function is a reflection of a graph over the line 𝑦 = 𝑥.
o Determining the equation of an inverse: Swop the 𝑥 and y’s around in your equation,
then, preferrably, you make y the subject.
o Sketching an inverse: Take the original graph’s coordinates and swop the 𝑥 and y values
around and draw the sketch.
o REMEMBER: Domain of original is Range of inverse and Range of original is Domain of
the inverse.
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