What is the value of cos(pi/9)cos((7pi)/(18))-sin(pi/9)sin((7pi)/(18)) ?

The value of cos(pi/9)cos((7pi)/(18))-sin(pi/9)sin((7pi)/(18)) is 0

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cos(pi/9)cos((7pi)/(18))-sin(pi/9)sin((7pi)/(18))

cos (\frac{π}{9}) cos (\frac{7 π}{18}) - sin (\frac{π}{9}) sin (\frac{7 π}{18})

0

Solution steps

cos (\frac{π}{9}) cos (\frac{7 π}{18}) - sin (\frac{π}{9}) sin (\frac{7 π}{18})

Rewrite using trig identities:

cos (\frac{π}{2})

= cos (\frac{π}{2})

Use the following trivial identity:

cos (\frac{π}{2}) = 0

= 0

2 sin (5) cos (5)

sin (2 arcsin (- \frac{5}{13}))

cot (6 5^{\circ})

cos^{2} (3 7^{\circ})

cos (\frac{5 π}{12}) - cos (\frac{π}{12})

What is the value of cos(pi/9)cos((7pi)/(18))-sin(pi/9)sin((7pi)/(18)) ?
The value of cos(pi/9)cos((7pi)/(18))-sin(pi/9)sin((7pi)/(18)) is 0