Is 1/(cot(θ))=(sec^2(θ)-1)/(tan(θ)) ?

The answer to whether 1/(cot(θ))=(sec^2(θ)-1)/(tan(θ)) is True

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prove 1/(cot(θ))=(sec^2(θ)-1)/(tan(θ))

Solution

prove

\frac{1}{cot ( θ )} = \frac{sec ^{2} ( θ ) - 1}{tan ( θ )}

Solution

True

Solution steps

\frac{1}{cot ( θ )} = \frac{sec ^{2} ( θ ) - 1}{tan ( θ )}

Manipulating left side

\frac{1}{cot ( θ )}

Express with sin, cos

\frac{1}{cot ( θ )}

Use the basic trigonometric identity:

cot (x) = \frac{cos ( x )}{sin ( x )}

= \frac{1}{\frac{c o s ( θ )}{s i n ( θ )}}

Simplify

\frac{1}{\frac{c o s ( θ )}{s i n ( θ )}} : \frac{sin ( θ )}{cos ( θ )}

\frac{1}{\frac{c o s ( θ )}{s i n ( θ )}}

Apply the fraction rule:

\frac{1}{\frac{b}{c}} = \frac{c}{b}

= \frac{sin ( θ )}{cos ( θ )}

= \frac{sin ( θ )}{cos ( θ )}

= \frac{sin ( θ )}{cos ( θ )}

Manipulating right side

\frac{sec ^{2} ( θ ) - 1}{tan ( θ )}

Express with sin, cos

\frac{- 1 + sec ^{2} ( θ )}{tan ( θ )}

Use the basic trigonometric identity:

sec (x) = \frac{1}{cos ( x )}

= \frac{- 1 + ( \frac{1}{c o s ( θ )} ) ^{2}}{tan ( θ )}

Use the basic trigonometric identity:

tan (x) = \frac{sin ( x )}{cos ( x )}

= \frac{- 1 + ( \frac{1}{c o s ( θ )} ) ^{2}}{\frac{s i n ( θ )}{c o s ( θ )}}

Simplify

\frac{- 1 + ( \frac{1}{c o s ( θ )} ) ^{2}}{\frac{s i n ( θ )}{c o s ( θ )}} : \frac{- cos ^{2} ( θ ) + 1}{cos ( θ ) sin ( θ )}

\frac{- 1 + ( \frac{1}{c o s ( θ )} ) ^{2}}{\frac{s i n ( θ )}{c o s ( θ )}}

Apply the fraction rule:

\frac{a}{\frac{b}{c}} = \frac{a \cdot c}{b}

= \frac{( - 1 + ( \frac{1}{c o s ( θ )} ) ^{2} ) cos ( θ )}{sin ( θ )}

(\frac{1}{cos ( θ )})^{2} = \frac{1}{cos ^{2} ( θ )}

(\frac{1}{cos ( θ )})^{2}

Apply exponent rule:

(\frac{a}{b})^{c} = \frac{a ^{c}}{b ^{c}}

= \frac{1 ^{2}}{cos ^{2} ( θ )}

Apply rule

1^{a} = 1

1^{2} = 1

= \frac{1}{cos ^{2} ( θ )}

= \frac{cos ( θ ) ( \frac{1}{c o s ^{2} ( θ )} - 1 )}{sin ( θ )}

Join

- 1 + \frac{1}{cos ^{2} ( θ )} : \frac{- cos ^{2} ( θ ) + 1}{cos ^{2} ( θ )}

- 1 + \frac{1}{cos ^{2} ( θ )}

Convert element to fraction:

1 = \frac{1 cos ^{2} ( θ )}{cos ^{2} ( θ )}

= - \frac{1 \cdot cos ^{2} ( θ )}{cos ^{2} ( θ )} + \frac{1}{cos ^{2} ( θ )}

Since the denominators are equal, combine the fractions:

\frac{a}{c} \pm \frac{b}{c} = \frac{a \pm b}{c}

= \frac{- 1 \cdot cos ^{2} ( θ ) + 1}{cos ^{2} ( θ )}

Multiply:

1 \cdot cos^{2} (θ) = cos^{2} (θ)

= \frac{- cos ^{2} ( θ ) + 1}{cos ^{2} ( θ )}

= \frac{\frac{- c o s ^{2} ( θ ) + 1}{c o s ^{2} ( θ )} cos ( θ )}{sin ( θ )}

Multiply

\frac{- cos ^{2} ( θ ) + 1}{cos ^{2} ( θ )} cos (θ) : \frac{- cos ^{2} ( θ ) + 1}{cos ( θ )}

\frac{- cos ^{2} ( θ ) + 1}{cos ^{2} ( θ )} cos (θ)

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{( - cos ^{2} ( θ ) + 1 ) cos ( θ )}{cos ^{2} ( θ )}

Cancel the common factor:

cos (θ)

= \frac{- cos ^{2} ( θ ) + 1}{cos ( θ )}

= \frac{\frac{- c o s ^{2} ( θ ) + 1}{c o s ( θ )}}{sin ( θ )}

Apply the fraction rule:

\frac{\frac{b}{c}}{a} = \frac{b}{c \cdot a}

= \frac{- cos ^{2} ( θ ) + 1}{cos ( θ ) sin ( θ )}

= \frac{- cos ^{2} ( θ ) + 1}{cos ( θ ) sin ( θ )}

= \frac{1 - cos ^{2} ( θ )}{cos ( θ ) sin ( θ )}

Rewrite using trig identities

\frac{1 - cos ^{2} ( θ )}{cos ( θ ) sin ( θ )}

Use the Pythagorean identity:

1 = cos^{2} (x) + sin^{2} (x)

1 - cos^{2} (x) = sin^{2} (x)

= \frac{sin ^{2} ( θ )}{cos ( θ ) sin ( θ )}

Cancel the common factor:

sin (θ)

= \frac{sin ( θ )}{cos ( θ )}

= \frac{sin ( θ )}{cos ( θ )}

We showed that the two sides could take the same form

\Rightarrow True

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Frequently Asked Questions (FAQ)

Is 1/(cot(θ))=(sec^2(θ)-1)/(tan(θ)) ?
The answer to whether 1/(cot(θ))=(sec^2(θ)-1)/(tan(θ)) is True