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Factoring and product formulas
Quadratic equations
Progressions
Trigonometry
Probability theory
Statistics
Circle
Triangles
Quadrangles, polygons
Shape Areas
Solid figures
Equations of geometric shapes
Various
Combinatorics
Vectors
Logarithms

Math formulas
Trigonometry
Cosine of double angle

Cosine of double angle

$cos(2\cdot a) = cos(a)^{2}-sin(a)^{2}$

Find

a

It is known that:

=

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