Is sin(2x)=(2cot(x))/(1+cot^2(x)) ?

The answer to whether sin(2x)=(2cot(x))/(1+cot^2(x)) is True

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prove sin(2x)=(2cot(x))/(1+cot^2(x))

Solution

prove

sin (2 x) = \frac{2 cot ( x )}{1 + cot ^{2} ( x )}

Solution

True

Solution steps

sin (2 x) = \frac{2 cot ( x )}{1 + cot ^{2} ( x )}

Manipulating right side

\frac{2 cot ( x )}{1 + cot ^{2} ( x )}

Express with sin, cos

\frac{2 cot ( x )}{1 + cot ^{2} ( x )}

Use the basic trigonometric identity:

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

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

Simplify

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

\frac{2 \cdot \frac{c o s ( x )}{s i n ( x )}}{1 + ( \frac{c o s ( x )}{s i n ( x )} ) ^{2}}

Apply exponent rule:

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

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

Multiply

2 \cdot \frac{cos ( x )}{sin ( x )} : \frac{2 cos ( x )}{sin ( x )}

2 \cdot \frac{cos ( x )}{sin ( x )}

Multiply fractions:

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

= \frac{cos ( x ) \cdot 2}{sin ( x )}

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

Apply the fraction rule:

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

= \frac{cos ( x ) \cdot 2}{sin ( x ) ( 1 + \frac{c o s ^{2} ( x )}{s i n ^{2} ( x )} )}

Join

1 + \frac{cos ^{2} ( x )}{sin ^{2} ( x )} : \frac{sin ^{2} ( x ) + cos ^{2} ( x )}{sin ^{2} ( x )}

1 + \frac{cos ^{2} ( x )}{sin ^{2} ( x )}

Convert element to fraction:

1 = \frac{1 sin ^{2} ( x )}{sin ^{2} ( x )}

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

Since the denominators are equal, combine the fractions:

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

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

Multiply:

1 \cdot sin^{2} (x) = sin^{2} (x)

= \frac{sin ^{2} ( x ) + cos ^{2} ( x )}{sin ^{2} ( x )}

= \frac{2 cos ( x )}{\frac{s i n ^{2} ( x ) + c o s ^{2} ( x )}{s i n ^{2} ( x )} sin ( x )}

Multiply

sin (x) \frac{sin ^{2} ( x ) + cos ^{2} ( x )}{sin ^{2} ( x )} : \frac{sin ^{2} ( x ) + cos ^{2} ( x )}{sin ( x )}

sin (x) \frac{sin ^{2} ( x ) + cos ^{2} ( x )}{sin ^{2} ( x )}

Multiply fractions:

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

= \frac{( sin ^{2} ( x ) + cos ^{2} ( x ) ) sin ( x )}{sin ^{2} ( x )}

Cancel the common factor:

sin (x)

= \frac{sin ^{2} ( x ) + cos ^{2} ( x )}{sin ( x )}

= \frac{2 cos ( x )}{\frac{s i n ^{2} ( x ) + c o s ^{2} ( x )}{s i n ( x )}}

Apply the fraction rule:

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

= \frac{cos ( x ) \cdot 2 sin ( x )}{sin ^{2} ( x ) + cos ^{2} ( x )}

= \frac{2 cos ( x ) sin ( x )}{sin ^{2} ( x ) + cos ^{2} ( x )}

= \frac{2 cos ( x ) sin ( x )}{cos ^{2} ( x ) + sin ^{2} ( x )}

Rewrite using trig identities

\frac{2 cos ( x ) sin ( x )}{cos ^{2} ( x ) + sin ^{2} ( x )}

Use the Double Angle identity:

2 sin (x) cos (x) = sin (2 x)

= \frac{sin ( 2 x )}{cos ^{2} ( x ) + sin ^{2} ( x )}

Use the Pythagorean identity:

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

= \frac{sin ( 2 x )}{1}

Apply rule

\frac{a}{1} = a

= sin (2 x)

= sin (2 x)

We showed that the two sides could take the same form

\Rightarrow True

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Frequently Asked Questions (FAQ)

Is sin(2x)=(2cot(x))/(1+cot^2(x)) ?
The answer to whether sin(2x)=(2cot(x))/(1+cot^2(x)) is True