Is sin(a)=(2tan(a/2))/(1+tan^2(a/2)) ?

The answer to whether sin(a)=(2tan(a/2))/(1+tan^2(a/2)) is True

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prove sin(a)=(2tan(a/2))/(1+tan^2(a/2))

Solution

prove

sin (a) = \frac{2 tan ( \frac{a}{2} )}{1 + tan ^{2} ( \frac{a}{2} )}

Solution

True

Solution steps

sin (a) = \frac{2 tan ( \frac{a}{2} )}{1 + tan ^{2} ( \frac{a}{2} )}

Let:

u = \frac{a}{2}

sin (2 u) = \frac{2 tan ( u )}{1 + tan ^{2} ( u )}

Prove

sin (2 u) = \frac{2 tan ( u )}{1 + tan ^{2} ( u )} :

True

sin (2 u) = \frac{2 tan ( u )}{1 + tan ^{2} ( u )}

Manipulating right side

\frac{2 tan ( u )}{1 + tan ^{2} ( u )}

Express with sin, cos

\frac{2 tan ( u )}{1 + tan ^{2} ( u )}

Use the basic trigonometric identity:

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

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

Simplify

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

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

Apply exponent rule:

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

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

Multiply

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

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

Multiply fractions:

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

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

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

Apply the fraction rule:

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

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

Join

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

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

Convert element to fraction:

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

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

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} ( u ) + sin ^{2} ( u )}{cos ^{2} ( u )}

Multiply:

1 \cdot cos^{2} (u) = cos^{2} (u)

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

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

Multiply

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

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

Multiply fractions:

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

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

Cancel the common factor:

cos (u)

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

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

Apply the fraction rule:

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

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

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

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

Rewrite using trig identities

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

Use the Double Angle identity:

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

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

Use the Pythagorean identity:

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

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

Apply rule

\frac{a}{1} = a

= sin (2 u)

= sin (2 u)

We showed that the two sides could take the same form

\Rightarrow True

Therefore

sin (a) = \frac{2 tan ( \frac{a}{2} )}{1 + tan ^{2} ( \frac{a}{2} )}

We showed that the two sides could take the same form

\Rightarrow True

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Frequently Asked Questions (FAQ)

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