Grade 11Trigonometry
Cos20+cos40+cos60-4cos10cos20cos30 equals to option (a) -1 option b -3/4 option c 1 option d 0
Cos20+cos40+cos60-4cos10cos20cos30 equals to option (a) -1 option b -3/4 option c 1 option d 0
2 Answers
poonam
Option a -1 first apply cosc+cosd on cos20+cos40 and then apply 2cosacosb on cos10cos20 solve It you will answer -1
mkmjnj
let us solve this question in parts
- cos20 + cos40 = 2cos30cos10
- 4cos10cos20cos30 = 2[ 2cos10cos20 ]cos30 = 2 [cos30 + cos10 ] cos30 = 2cos30cos30 + 2cos10cos30
- cos60 = ½
now solve them by putting these values in question
you will get ANS = 1
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