What is the value of cos(765) ?

The value of cos(765) is (sqrt(2))/2

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cos(765)

cos (76 5^{\circ})

\frac{2}{2}

Decimal Notation

0.70710 \dots

Solution steps

cos (76 5^{\circ})

cos (76 5^{\circ}) = cos (4 5^{\circ})

cos (76 5^{\circ})

Rewrite

76 5^{\circ}

36 0^{\circ} \cdot 2 + 4 5^{\circ}

= cos (36 0^{\circ} 2 + 4 5^{\circ})

Apply the periodicity of

cos

cos (x + 36 0^{\circ} \cdot k) = cos (x)

cos (36 0^{\circ} \cdot 2 + 4 5^{\circ}) = cos (4 5^{\circ})

= cos (4 5^{\circ})

= cos (4 5^{\circ})

Use the following trivial identity:

cos (4 5^{\circ}) = \frac{2}{2}

cos (4 5^{\circ})

cos (x)

periodicity table with

36 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= \frac{2}{2}

= \frac{2}{2}

\frac{10}{tan ( 3 5 ^{\circ} )}

cos (3 0^{\circ}) \cdot 40

cos (3 0^{\circ}) \cdot 12

sec^{2} (\frac{π}{4}) - 1

\frac{6}{tan ( 6 0 ^{\circ} )}