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Byju's Answer
Standard VIII
Mathematics
Expansion of (a-b)^3
If a- 1/a=4 a...
Question
If a-
1
a
= 4 and
a
≠
0
; then
a
3
−
1
a
3
is equal to
A
72
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B
56
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C
76
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D
91
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Solution
The correct option is
C
76
Given that
a
−
1
a
=
4
(
a
−
1
a
)
3
=
(
a
)
3
−
(
1
a
)
3
−
3
×
a
×
1
a
(
a
−
1
a
)
(
a
)
3
−
(
1
a
)
3
=
(
a
−
1
a
)
3
+
3
(
a
−
1
a
)
(
a
)
3
−
(
1
a
)
3
=
64
+
12
......[ since
a
−
1
a
=
4
]
(
a
)
3
−
(
1
a
)
3
=
76
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