What is the value of cos((7pi)/(21)) ?

The value of cos((7pi)/(21)) is 1/2

English

Español

Português

Français

Deutsch

Italiano

Русский

中文(简体)

한국어

日本語

Tiếng Việt

עברית

العربية

Popular >

cos((7pi)/(21))

cos (\frac{7 π}{21})

\frac{1}{2}

Decimal Notation

0.5

Solution steps

cos (\frac{7 π}{21})

Simplify:

\frac{7 π}{21} = \frac{π}{3}

\frac{7 π}{21}

Cancel the common factor:

7

= \frac{π}{3}

= cos (\frac{π}{3})

Use the following trivial identity:

cos (\frac{π}{3}) = \frac{1}{2}

cos (\frac{π}{3})

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= \frac{1}{2}

= \frac{1}{2}

cot (1 2^{\circ})

sin (2 πi)

cos (arccos (- 0.6))

1.5 \cdot sin (3 0^{\circ})

sin (\frac{1}{2} arcsin (- \frac{7}{25}))