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Question of 100

Q.(i) Draw the graph of the function f:R→Rf : R \to R defined by f(x)=∣x∣f(x) = |x|.

(3)
(ii) Let A = {1,2,3,4,5,6}\{1, 2, 3, 4, 5, 6\} and R is a relation defined from A to A by
R={(x,y):y=x+1}R = \{(x, y) : y = x + 1\}
(a) Depict this relation using an arrow diagram.
(2)
(b) Write the domain of R. (1)
Kerala DhseKerala DHSE Plus One Board 2021Subjective· 6mImportance★★★★★
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Figure — Part (i) explicitly instructs 'Draw the graph of f(x)=|x|', a hard draw-keyword; the canonical modulus-functio
Figure — Part (i) explicitly instructs 'Draw the graph of f(x)=|x|', a hard draw-keyword; the canonical modulus-functio

The graph of f(x)=∣x∣f(x)=|x| is a V-shaped curve made of two rays meeting at the origin. For the relation R={(x,y):y=x+1}R=\{(x,y): y=x+1\} on A={1,2,3,4,5,6}A=\{1,2,3,4,5,6\}, only pairs where both xx and x+1x+1 lie in AA survive, giving 5 ordered pairs and domain {1,2,3,4,5}\{1,2,3,4,5\}.

(i) Graph of f(x)=∣x∣f(x) = |x|

The modulus function is defined piecewise:

f(x)=∣x∣={x,x≥0−x,x<0f(x) = |x| = \begin{cases} x, & x \ge 0 \\ -x, & x < 0 \end{cases}

A table of values:

xx−3-3−2-2−1-100112233
f(x)f(x)33221100112233

Plotting these points: for x≥0x \ge 0 the graph is the straight line y=xy=x (a ray from the origin going up-right at 45∘45^\circ to the xx-axis); for x<0x<0 it is the straight line y=−xy=-x (a ray from the origin going up-left, also at 45∘45^\circ to the xx-axis). The two rays meet at the origin (0,0)(0,0), forming a symmetric V-shape that is symmetric about the yy-axis (since f(−x)=f(x)f(-x)=f(x)). The graph lies entirely in the region y≥0y \ge 0; its domain is R\mathbb{R} and its range is [0,∞)[0,\infty).

(ii) The relation R={(x,y):y=x+1}R = \{(x,y): y = x+1\} on A={1,2,3,4,5,6}A=\{1,2,3,4,5,6\}

Check each x∈Ax \in A to see whether y=x+1y=x+1 also lies in AA:

  • x=1⇒y=2∈Ax=1 \Rightarrow y=2 \in A -> (1,2)(1,2)
  • x=2⇒y=3∈Ax=2 \Rightarrow y=3 \in A -> (2,3)(2,3)
  • x=3⇒y=4∈Ax=3 \Rightarrow y=4 \in A -> (3,4)(3,4)
  • x=4⇒y=5∈Ax=4 \Rightarrow y=5 \in A -> (4,5)(4,5)
  • x=5⇒y=6∈Ax=5 \Rightarrow y=6 \in A -> (5,6)(5,6)
  • x=6⇒y=7∉Ax=6 \Rightarrow y=7 \notin A -> rejected

So R={(1,2),(2,3),(3,4),(4,5),(5,6)}R = \{(1,2), (2,3), (3,4), (4,5), (5,6)\}.

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