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Byju's Answer
Standard X
Mathematics
Relation between Trigonometric Ratios
Prove that: 7...
Question
Prove that:
7
π
12
+
cos
π
12
=
sin
5
π
12
-
sin
π
12
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Solution
105
°
=
7
π
12
,
15
°
=
π
12
,
75
°
=
5
π
12
,
15
°
=
π
12
LHS = cos105
o
+ cos15
o
= cos(90
o
+ 15
o
) + cos(90
o
-
75
o
)
= - sin 15
o
+ sin 75
o
[As cos(90
o
+A) =
-
sin A and cos(90
o
-
B) = sin B]
= sin 75
o
-
sin 15
o
= RHS
Hence proved.
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4
Similar questions
Q.
The value of
cos
π
12
-
sin
π
12
is ______________.
Q.
Prove that:
(i) cos 55° + cos 65° + cos 175° = 0
(ii) sin 50° − sin 70° + sin 10° = 0
(iii) cos 80° + cos 40° − cos 20° = 0
(iv) cos 20° + cos 100° + cos 140° = 0
(v)
sin
5
π
18
-
cos
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π
9
=
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sin
π
9
(vi)
cos
π
12
-
sin
π
12
=
1
2
(vii) sin 80° − cos 70° = cos 50°
(viii) sin 51° + cos 81° = cos 21°
Q.
If
X
=
sin
(
θ
+
7
π
12
)
+
sin
(
θ
−
π
12
)
+
sin
(
θ
+
3
π
12
)
,
Y
=
cos
(
θ
+
7
π
12
)
+
cos
(
θ
−
π
12
)
+
cos
(
θ
+
3
π
12
)
,
then prove that
X
Y
−
Y
X
=
2
tan
2
θ
.
Q.
Prove that
(
3
-
5
)
is irrational.
Or, prove that
2
2
3
is irrational.
Q.
Prove that
(
5
-
3
)
is irrational.
Or, prove that
3
3
5
is irrational.
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