What is the value of cos(65)cos(20)+sin(65)sin(20) ?

The value of cos(65)cos(20)+sin(65)sin(20) is (sqrt(2))/2

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cos(65)cos(20)+sin(65)sin(20)

cos (6 5^{\circ}) cos (2 0^{\circ}) + sin (6 5^{\circ}) sin (2 0^{\circ})

\frac{2}{2}

Decimal Notation

0.70710 \dots

Solution steps

cos (6 5^{\circ}) cos (2 0^{\circ}) + sin (6 5^{\circ}) sin (2 0^{\circ})

Rewrite using trig identities:

cos (4 5^{\circ})

cos (6 5^{\circ}) cos (2 0^{\circ}) + sin (6 5^{\circ}) sin (2 0^{\circ})

Use the Angle Difference identity:

cos (s) cos (t) + sin (s) sin (t) = cos (s - t)

= cos (6 5^{\circ} - 2 0^{\circ})

Simplify

= 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}

arcsin (1.06)

cos (0) \cdot cos (0)

cos (\frac{5}{4}) π

arctan (\frac{- 5}{8})

\frac{1.5 \cdot 25}{cos ( 16.8 2 ^{\circ} )}

What is the value of cos(65)cos(20)+sin(65)sin(20) ?
The value of cos(65)cos(20)+sin(65)sin(20) is (sqrt(2))/2