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cos 72° + cos 144°
= 2cos108°cos36°
=2(-0.309)(0.809)
=-0.4999
=-0.5
(Since 360°/5=72°)
cos(72°) + cos(144°) + cos(216°) + cos(288°) + cos(360°) = 0
cos(288°) = cos(360°-288°) = cos(72°)
cos(216°) = cos(360°-216°) = cos(144°)
cos(360°) = 1
Applying these substitutions,
2*cos(72°) + 2*cos(144°) + 1 = 0
Thus
cos(72°) + cos(144°) = -1/2
= 2cos108°cos36°
=2(-0.309)(0.809)
=-0.4999
=-0.5
(Since 360°/5=72°)
cos(72°) + cos(144°) + cos(216°) + cos(288°) + cos(360°) = 0
cos(288°) = cos(360°-288°) = cos(72°)
cos(216°) = cos(360°-216°) = cos(144°)
cos(360°) = 1
Applying these substitutions,
2*cos(72°) + 2*cos(144°) + 1 = 0
Thus
cos(72°) + cos(144°) = -1/2
shivam9640:
ans is -0.5
yes sorry for the mistake.. i corrected it
cos108 ke value bena use keye ne ho skta
check the ans now
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