Question

посчитать, на фотографии​

Answer 1

Ответ:

$frac{1}{2}$

Объяснение:

$1)cos(frac{pi}{11} )+cos(frac{3pi}{11} )+cos(frac{5pi}{11} )+cos(frac{7pi}{11} )+cos(frac{9pi}{11} )=\=frac{2sin(frac{pi}{11})cos(frac{3pi}{11} )+sin(frac{2}{11} )2sin(frac{pi}{11} )cos(frac{5pi}{11} )+2sin(frac{pi}{11} )cos(frac{7pi}{11} )+2sin(frac{pi}{11} ) cos(frac{9pi}{11} )}{2cos(frac{pi}{11} ) } =\=2sin(frac{pi}{11} )cos(frac{9pi}{11} )=-sin(frac{8pi}{11} )+sin(frac{10pi}{11} )=frac{sin(frac{10pi}{11} )}{2sin(frac{2pi}{11} )} =frac{1}{2}$

$2)H=cos(frac{pi}{11} )+cos(frac{3pi}{11} )+cos(frac{5pi}{11} )+cos(frac{7pi}{11} )+cos(frac{9pi}{11} )\H=cos(-frac{pi}{11} )+cos(-frac{3pi}{11} )+cos(-frac{5pi}{11} )+cos(-frac{7pi}{11} )+cos(-frac{9pi}{11} )\-1=cos(-frac{11pi}{11} )\2H-1=>H=frac{1}{2}$