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Byju's Answer
Standard XII
Mathematics
Complex Numbers
If coslog i4 ...
Question
If
cos
(
log
i
4
i
)
=
a
+
b
i
, then
A
a
=
1
,
b
=
2
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B
a
=
1
,
b
=
−
1
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C
a
=
−
1
,
b
=
1
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D
a
=
1
,
b
=
0
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Solution
The correct option is
D
a
=
1
,
b
=
0
Given
cos
(
log
i
4
i
)
=
a
+
b
i
⇒
a
+
b
i
=
cos
(
4
i
log
i
)
i
=
e
i
π
/
2
⇒
log
i
=
i
π
2
So,
a
+
b
i
=
cos
(
4
i
×
i
π
2
)
⇒
a
+
b
i
=
1
Hence,
a
=
1
,
b
=
0
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0
Similar questions
Q.
If
3
-
1
3
+
1
=
a
-
b
3
, then
(a) a = 2, b =1
(b) a = 2, b =−1
(c) a = −2, b = 1
(d) a = b = 1