Question

demostrati ca :cos 35+cos 65+ cos 90 + cos 115+ cos 145=0

Answer 1

Răspuns:

Explicație pas cu pas:

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Spor

Answer 2

$\it cos115^o=-cos(180^o-115^o)=-cos65^o\\ \\ cos145^o=-cos(180^o-145^o)=-cos35^o\\ \\ cos90^o=0$

Expresia din enunț devine:

$\it cos35^o+cos65^o +0-cos65^o-cos35^o=0 \Leftrightarrow 0=0\ \ (A)$