CBSE Class 12 Math 2020 Delhi Set 1 Solved Paper

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Section - B

Q. Nos. 21 to 26 carry 2 marks each.
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Question : 21 of 36
 
Marks: +1, -0
If f(x)=4x+36x4,x23, then show that (fof) (x)=x, for all x23. Also, write inverse of f.
OR
Check if the relation R in the set of real numbers defined as R={(a,b):a<b} is (i) symmetric, (ii) transitive
Solution:
f(x)=4x+36x4
ff(x)=4(4x+36x4)+36(4x+36x4)4
=16x+12+18x1224x+1824+16
=34x34=x
y=4x+36x4
6xy4y=4x+3
6xy4x=4y+3
x=4y+36y4
f(x)=4x+36x4
OR
Given : R={(a,b):a<b}
Let A be the set of real numbers.
(i) For symmetric : Let a,bA
Then, (a,b)R such that a<b
b<a which is false
(b,a)R
R is not symmetric.
(ii) For transitive : Let a,b,cA
Then, (a,b)R and (b,c)R
a<b and b<c
a<c
(a,c)R
R is transitive.
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