In mathematics, trigonometric identities are equalities that involvetrigonometric functions and are true for every single value of the occurringvariables. Geometrically, these are identities involving certain functions of one or more angles. They are distinct from triangle identities, which are identities involving both angles and side lengths of a triangle. Only the former are covered in this article.

Logarithmic equations contain logarithmic expressions and constants. A logarithm is another way to write an exponent and is defined by  if and only if . When one side of the equation contains a single logarithm and the other side contains a constant, the equation can be solved by rewriting the equation as an equivalent exponential equation using the definition of logarithm from above. For example, ; ; . If one side of a logarithmic equation contains more than one logarithm, use the properties of logarithms to condense it into a single logarithm. Properties of logarithms basically change multiplication into addition, division into subtraction, exponent into multiplication, and radical into division.
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