What is the value of cos(pi/9)cos((2pi)/9)-sin(pi/9)sin((2pi)/9) ?

The value of cos(pi/9)cos((2pi)/9)-sin(pi/9)sin((2pi)/9) is 1/2

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cos(pi/9)cos((2pi)/9)-sin(pi/9)sin((2pi)/9)

cos (\frac{π}{9}) cos (\frac{2 π}{9}) - sin (\frac{π}{9}) sin (\frac{2 π}{9})

\frac{1}{2}

Solution steps

cos (\frac{π}{9}) cos (\frac{2 π}{9}) - sin (\frac{π}{9}) sin (\frac{2 π}{9})

Rewrite using trig identities:

cos (\frac{π}{3})

= cos (\frac{π}{3})

Use the following trivial identity:

cos (\frac{π}{3}) = \frac{1}{2}

= \frac{1}{2}

csc (3 9^{\circ})

24 tan (7 0^{\circ})

arctan (\frac{60}{40})

sin (\frac{5 π}{5})

2 π - sin (2 π)

What is the value of cos(pi/9)cos((2pi)/9)-sin(pi/9)sin((2pi)/9) ?
The value of cos(pi/9)cos((2pi)/9)-sin(pi/9)sin((2pi)/9) is 1/2