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If a + b + c = 3 and none of a, b and c is equal to 1, what is the value of

1(1a)(1b)+1(1b)(1c)+1(1c)(1a)?\frac{1}{(1-a)(1-b)}+\frac{1}{(1-b)(1-c)}+\frac{1}{(1-c)(1-a)} ?

a

0

b

1

c

3

d

6

Answer : Option A
Explanation :

a + b + c = 3

1(1a)(1b)+1(1b)(1c)+1(1c)(1a)\therefore \frac{1}{(1-a)(1-b)}+\frac{1}{(1-b)(1-c)}+\frac{1}{(1-c)(1-a)}

=1c+1a+1b(1a)(1b)(1c)=3(a+b+c)(1a)(1b)(1c)=\frac{1-c+1-a+1-b}{(1-a)(1-b)(1-c)}=\frac{3-(a+b+c)}{(1-a)(1-b)(1-c)}

=33(1a)(1b)(1c)=0=\frac{3-3}{(1-a)(1-b)(1-c)}=0

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