IIT JEE , AIEEE Forum - Mathematics , Trignometry

iit009

Q1. (1+cos(pi/8)(1+cos(3pi/8)(1+cos(5pi/8)(1+cos(7pi/8) is equal to....
Q2. The number of all possible triplets(a,b,c) such that a+bcos2x +csin^2x=0 for all x is......
Q3. The sides of the triangle inscribed in a circle subtend angles A,B,C at the centre.The minimuvalue of the arithmetic mean of cos(A+pi/2), cos(B+pi/2), cos(C+pi/2) is equal to...........

Q4. without using tables prove that sin12sin48sin54=1/8

ashish_banga

is the answer to 3 = -3/2

iit009

sorry answer is -squareroot(3)/2

ramkumar_november

for the first question the answer is 1\8 ..... for proof go to this link

http://www.goiit.com/posts/list/trignometry-trigonometry-question-51296.htm

second question

cos2x=1-2sin²x

1-cos2x-2sin²x=0

so a=1,b=-1,c=-2 ..

only one triplet is possible

allamraju

Q1.(1+cospi/8)(1-cospi/8)(1+cos3pi/8)(1-cos3pi/8)

=sin^2pi/8.sin^2 3pi/8

=1/4(cospi/4-cospi/2)²

^=1/8

^{pls rate me if i am correct}

iit009

please answer

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