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ISI Entrance Examination
2012 ISI Entrance Examination
1
trigonometric identity..... isi 2012 #1
trigonometric identity..... isi 2012 #1
Source:
May 13, 2012
trigonometry
Problem Statement
i)If
X
,
Y
,
Z
X,Y,Z
X
,
Y
,
Z
be the angles of a triangle then show that
tan
X
2
tan
Y
2
+
tan
Y
2
tan
Z
2
+
tan
Z
2
tan
X
2
=
1
\tan {\frac{X}{2}}\tan {\frac{Y}{2}}+\tan {\frac{Y}{2}}\tan {\frac{Z}{2}}+\tan {\frac{Z}{2}}\tan {\frac{X}{2}}=1
tan
2
X
tan
2
Y
+
tan
2
Y
tan
2
Z
+
tan
2
Z
tan
2
X
=
1
ii) Prove using (i) or otherwise that
tan
X
2
tan
Y
2
tan
Z
2
≤
1
3
3
\tan {\frac{X}{2}}\tan {\frac{Y}{2}}\tan {\frac{Z}{2}}\leq\frac {1}{3\sqrt{3}}
tan
2
X
tan
2
Y
tan
2
Z
≤
3
3
1
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