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  1. If ab + bc + ca = 0 then the value of
    1
    +
    1
    +
    1
    is
    ( a² - bc )( b² - ac )( c² - ab )

    1. 0
    2. 1
    3. 3
    4. a + b + c
Correct Option: A

ab + bc + ca = 0
⇒ ab + ca = – bc
∴ a2 – bc = a2 + ab + ac = a(a + b + c)
Similarly,
b2 – ca = b(a + b + c)
c2 – ab = c(a + b + c)

∴ Expression =
1
+
1
+
1
( a² - bc )( b² - ac )( c² - ab )

Expression =
1
+
1
+
1
a(a + b + c)b(a + b + c)c(a + b + c)

Expression =
1
1
+
1
+
1
(a + b + c)abc

Expression =
1
bc + ca + ab
(a + b + c)abc

Expression =
1
×
0
= 0
(a + b + c)abc



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