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Byju's Answer
Standard XII
Mathematics
Differentiation Using Substitution
If 12 sin x-9...
Question
If 12 sin x − 9sin
2
x attains its maximum value at x = α, then write the value of sin α.
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Solution
Let
f
x
=
12
sin
x
-
9
sin
2
x
=
-
9
sin
2
x
-
12
sin
x
=
-
3
sin
x
2
-
2
.
3
sin
x
.
2
+
2
2
-
4
=
-
3
sin
x
-
2
2
-
4
=
4
-
3
sin
x
-
2
2
Minimum
value
of
3
sin
x
-
2
2
is
0
.
Therefore
,
maximum
value
of
f
x
=
4
-
3
sin
x
-
2
2
is
4
.
We
are
given
that
12
sin
x
-
9
sin
2
x
will
attain
its
maximum
value
at
x
=
α
.
∴
12
sin
α
-
9
sin
2
α
=
4
⇒
-
9
sin
2
α
+
12
sin
α
-
4
=
0
⇒
9
sin
2
α
-
12
sin
α
+
4
=
0
⇒
9
sin
2
α
-
6
sin
α
-
6
sin
α
+
4
=
0
⇒
3
sin
α
3
sin
α
-
2
-
2
3
sin
α
-
2
=
0
⇒
3
sin
α
-
2
3
sin
α
-
2
=
0
∴
sin
α
=
2
3
Suggest Corrections
6
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