What is the value of 4cos((5pi)/6) ?

The value of 4cos((5pi)/6) is -2sqrt(3)

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4cos((5pi)/6)

4 cos (\frac{5 π}{6})

- 23

Decimal Notation

- 3.46410 \dots

Solution steps

4 cos (\frac{5 π}{6})

Use the following trivial identity:

cos (\frac{5 π}{6}) = - \frac{3}{2}

cos (\frac{5 π}{6})

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{3}{2}

= 4 (- \frac{3}{2})

Simplify

4 (- \frac{3}{2}) : - 23

4 (- \frac{3}{2})

Remove parentheses:

(- a) = - a

= - 4 \cdot \frac{3}{2}

Multiply fractions:

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

= - \frac{3 \cdot 4}{2}

Divide the numbers:

\frac{4}{2} = 2

= - 23

= - 23

tan (- \frac{7 π}{3})

15 \cdot cos (6 0^{\circ})

6 cos (16 0^{\circ})

arctan (tan (\frac{π}{2}))

sin (58 5^{\circ})