Fermi
·
Concept Library
·
Courses
·
Books
·
Problems
·
Simulations
·
Math Wiki
·
High School
Fermi
›
Problems
Mathematics
Mathematics
Problem
Derive the identity
cos
2
x
=
1
−
tan
2
x
1
+
tan
2
x
\displaystyle \cos 2x = \frac{1-\tan^{2}x}{1+\tan^{2}x}
cos
2
x
=
1
+
tan
2
x
1
−
tan
2
x
.
Browse the problem library