Question

Show that Cos40° + Cos 80° + Cos 160º = 0​

Answer 1

Answer:

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Step-by-step explanation:

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Answer 2

Answer:

cos a +cos b= 2cos{(a+b)/2}*cos{(a-b)/2}

a=40, b=80;

2cos{(40+80)/2}*cos{(40-80)/2}+cos 160

2cos(120/2)cos(-40/2)+cos160

2cos60cos(-20)+cos(180-20)

2*(1/2)cos20-cos20

cos20-cos20

=0;

​