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Functions — Class 11 Maharashtra HSC Mathematics revision notes

A 5-page visual revision sheet for Functions, written for Class 11 Maharashtra HSC Mathematics. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.

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Functions in one look

one rule, one output for every input: domain, range and the shapes that follow

Function, Domain, Co-domain, Range

  • a function f:Ato B sends each x in A to exactly one y in B, y=f(x)
  • A is the domain of f, B the co-domain, y is the image of x
  • range = f(A): every y actually hit, always a subset of the co-domain
  • vertical line test: no vertical line may cut the graph of a function twice
  • horizontal line test: no horizontal line may cut the graph twice, so f is one-one

One-one and onto

  • one-one (injective): different elements of A have different images, f(a)=f(b)⇒ a=b
  • onto (surjective): every y in B is the image of some x in A, so f(A)=B
  • range of f = f(A) subset co-domain of f, with equality exactly when f is onto

The four combinations

  • one-one, not onto: every arrow lands on a different target, but some targets are unused
  • one-one and onto: a bijection: every target hit exactly once
  • onto, not one-one: every target is hit, but some target is hit twice
  • neither one-one nor onto: some target unused, another hit more than once

Worked: evaluating a function

Q. if f(x)=2x^2-3x+4, find f(7) and f(-2t)

  1. f(7)=2(7)^2-3(7)+4=2(49)-21+4
  2. =98-21+4=81
  3. f(-2t)=2(-2t)^2-3(-2t)+4=2(4t^2)+6t+4

Answer: f(7)=81, f(-2t)=8t^2+6t+4

Six ways to represent a function

  • verbal: a sentence describing the rule, e.g. output exceeds twice the input by 1
  • arrow/Venn diagram: domain and range as two ovals joined by arrows
  • ordered pairs: pairs like (2,5),(3,7),(4,9),(5,11); domain is the 1st entries, range the 2nd
  • rule/formula: y=f(x)=2x+1, with a stated domain
  • tabular: a two-row table of x and y values
  • graphical: domain is the graph's projection on the X-axis, range its projection on the Y-axis

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