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Mathematics
Problem
In Exercises 11-51, prove the identity. 17.
cos
2
x
−
1
cos
x
=
−
tan
x
sin
x
\frac{\cos ^{2} x-1}{\cos x}=-\tan x \sin x
c
o
s
x
c
o
s
2
x
−
1
=
−
tan
x
sin
x
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