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Math Aa HL Ch. 3 Notes

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IB Math AA HL Chapter 3 Functions Notes

A function is a mathematical rule. Although the word “function” is often used for any
mathematical rule, this is not strictly correct. For a mathematical rule to be a function, each value
of x can have only one image.

Vocabulary:
Domain – the set of numbers that provide the input for the rule.
Image – the output from the rule of an element in the domain.
Range – the set of numbers consisting of the images of the domain.
Co-domain – a set containing the range.
Function – a rule that links each member of the domain to exactly one member of the range.

Two types of notations for functions exist, they are f(x) = ax + b or f:x → ax + b

Review the different types of numbers.

Composite functions: one function followed by another f  g  x   or f  g  x 


The order is important f  g  x    g  f  x   accept in rare cases.

Inverse functions: An inverse function is the reverse of the function. It allows one to find the
input when they start with the output. f 1  x  means the inverse of f  x 

How to find an inverse:


1. Check that an inverse function exists for the given domain.
2. Rearrange the function so that the subject is x.
3. Interchange x and y.

The graph of inverse functions.


The graph is the reflection over the y = x line.
If a point on the graph is (x, y) then the point on the inverse is (y, x).
Reciprocal functions Absolute value function or piecewise function
1  x, x  0
f  x  f  x  x or f  x  
x   x, x  0
Vertical asymptotes
x ≠ 0 or denominator ≠ 0

Drawing a graph:
Roots – value of x when y = 0
y-intercept – the value of y when x = 0
turning points – vertex or where the graph changes direction
vertical asymptotes – when y is not defined
horizontal asymptotes – when x → ∞

Transformations:
For kf(x), each y-value is multiplied by k and so this creates a vertical stretch.
For f(kx), each x-value is multiplied by k and so this creates a horizontal stretch.
For f  x   k , k is added to each y-value and so the graph is shifted vertically.
For f  x  k  , k is added to each x-value and so the graph is shifted horizontally.
For  f  x  , each y-value is multiplied by -1 and so each point is reflected in the x-axis.
For f   x  , each x-value is multiplied by -1 and so each point in reflected in the y-axis.

g  x a bx  c
Rational Functions f  x   specifically f  x   and f  x  
h x  px  q px  q
a 1
f  x  this is a transformation of a reciprocal function f  x  
px  q x

bx  c a
f  x  this is similar to f  x   but it has a horizontal asymptotes.
px  q px  q
b b
Horizontal asymptotes y  as when x → ∞, y 
p p
Even and Odd functions:
A function is odd. if for all x in the domain, f(-x) = -f(x). Symmetric about the origin
A function is even, if for all x in the domain, f(-x) = f(x). Symmetric across the y-axis

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