Sign of Quotient of Factors of Difference of Squares/Corollary
Jump to navigation
Jump to search
Corollary to Sign of Quotient of Factors of Difference of Squares
Let $a, b \in \R$ such that $a \ne b$.
Then
- $-\map \sgn {\dfrac {b - a} {b + a} } = \map \sgn {a^2 - b^2} = -\map \sgn {\dfrac {b + a} {b - a} }$
where $\sgn$ denotes the signum of a real number.
Proof
\(\ds \map \sgn {\frac {b - a} {b + a} }\) | \(=\) | \(\ds \map \sgn {\paren {-1} \frac {a - b} {a + b} }\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \map \sgn {-1} \map \sgn {\frac {a - b} {a + b} }\) | Signum Function is Completely Multiplicative | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {-1} \map \sgn {\frac {a - b} {a + b} }\) | Definition of Signum Function | |||||||||||
\(\ds \) | \(=\) | \(\ds -\map \sgn {a^2 - b^2}\) | Sign of Quotient of Factors of Difference of Squares | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {-1} \map \sgn {\frac {a + b} {a - b} }\) | Sign of Quotient of Factors of Difference of Squares | |||||||||||
\(\ds \) | \(=\) | \(\ds \map \sgn {-1} \map \sgn {\frac {a + b} {a - b} }\) | Definition of Signum Function | |||||||||||
\(\ds \) | \(=\) | \(\ds \map \sgn {\paren {-1} \frac {a + b} {a - b} }\) | Signum Function is Completely Multiplicative | |||||||||||
\(\ds \) | \(=\) | \(\ds \map \sgn {\frac {b + a} {b - a} }\) |
$\blacksquare$