Class 11 › Mathematics Relations and Functions Class 11 Mathematics · Chapter 2
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Browse all 60 kits → SummaryThis chapter links pairs of objects from two sets. The Cartesian product \(A\times B=\{(a,b):a\in A,\ b\in B\}\) collects all ordered pairs; two ordered pairs are equal iff their first and second elements match, and if \(n(A)=p,\ n(B)=q\) then \(n(A\times B)=pq\). A relation \(R\) from \(A\) to \(B\) is any subset of \(A\times B\); its domain is the set of first elements, its range the set of second elements, with the whole \(B\) as codomain (range \(\subset\) codomain). The total number of relations is \(2^{pq}\). A function is a special relation in which every element of the domain has exactly one image. The book studies real functions and graphs of the identity, constant, polynomial, rational, modulus \(|x|\), signum and greatest-integer \([x]\) functions. It also defines algebra of real functions: for \(f,g:X\to\mathbb{R}\), \((f+g)(x)=f(x)+g(x)\), \((f-g)(x)=f(x)-g(x)\), \((fg)(x)=f(x)g(x)\), \((kf)(x)=kf(x)\) and \((f/g)(x)=f(x)/g(x)\) when \(g(x)\ne 0\). These ideas make functions a precise language for the rest of mathematics.
Cartesian product of sets Ordered pairs and equality Relations: domain, range, codomain Functions as special relations Identity, constant and polynomial functions Modulus, signum and greatest integer functions Algebra of real functions Key termsOrdered pair
A pair \((a,b)\) in which order matters; \((a,b)=(c,d)\) iff \(a=c,\ b=d\).
Cartesian product
\(A\times B=\{(a,b):a\in A,\ b\in B\}\), with \(n(A\times B)=n(A)\,n(B)\).
Relation
A subset of \(A\times B\) describing a link between elements of \(A\) and \(B\).
Function
A relation in which each element of the domain has one and only one image.
Domain, range, codomain
Set of first elements (domain), set of second elements (range), and the whole set \(B\) (codomain).
Modulus function
\(f(x)=|x|\), equal to \(x\) for \(x\ge 0\) and \(-x\) for \(x<0\).
Extra questions & answersQ1 If \(n(A)=3\) and \(B=\{3,4,5\}\), how many elements has \(A\times B\)? Answer Q2 Define a function from set \(A\) to set \(B\). Answer Q3 Give the number of relations from \(A\) to \(B\) when \(n(A)=p,\ n(B)=q\). Answer Q4 Find the domain and range of \(f(x)=\sqrt{9-x^2}\). Answer Q5 Describe the signum function and its range. Answer Q6 Write the greatest integer function and the values of \([2.7]\) and \([-1.2]\). Answer Q7 If \((x+1,\,y-2)=(3,1)\), find \(x\) and \(y\). Answer Q8 Is \(A\times B=B\times A\) in general? Explain. Answer Q9 For \(f(x)=x^2\) and \(g(x)=2x+1\), write \((fg)(x)\). Answer Q10 Define a real function and a real valued function. Answer Try one from this chapter
If \(n(A)=3\) and \(n(B)=2\), then \(n(A\times B)\) is:
A 8 B 9 C 6 D 5
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