and 
prove
that 
OR
In an acute angled 
if
tan 
and sec
Find
the value of 
and 
Answer:
We have to find cos2 A in terms of m
and n. This means that the angle B is to be eliminate from the
given relations.
Now, 
and 
(1)
On substituting the values of 
and
in 
we get
(1)
(1)
(1)
Hence Proved
OR
We have, 
and
and
?(i)
and 
?(ii)(1)
Adding Eqs. (i) and (ii), we get
(1/2)
Putting 
in
Eq. (ii), we get
?(iii)(1/2)
In 
?(iv)(1/2)
Adding Eq. (iii) and (iv), we get
Putting the value of C in Eq. (iv), we get
(1/2)
Hence, 
(1/2)
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