cos20 cos40 cos80=1/16
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Answered by
17
see my answer !!!!!!!!
I think question should be
cos20 cos40 cos 60 cos80 = 1/16
you didn't write cos60
no problems
don't do next time wrong
OK
I think question should be
cos20 cos40 cos 60 cos80 = 1/16
you didn't write cos60
no problems
don't do next time wrong
OK
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Nikki57:
Abhinash bhaiya kya writing hai :D
Answered by
6
Hey there !!!!!
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=cos20cos40cos60cos80
Multiply and divide with 2sin20
=2sin20cos20cos40cos60cos80/2sin20
We know that 2sinAcosA = sin 2A
So 2sin20cos20 = sin2*20 =sin40
= sin40cos40cos60cos80/2sin20
Multiply and divide with "2"
= 2sin40cos40cos60cos80/2*2sin20
=cos60sin80cos80/2*2sin20
Multiply and divide with "2"
= cos60*2sin80cos80/8sin20
= cos60sin160/8sin20
We know that
sin(180-∅) = sin∅
So sin160 = sin(180-20) = sin20
So,
= cos60sin160/8sin20
=cos60sin20/8sin20
= cos60/8
cos60 = 1/2
= 1/16
LHS = RHS
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=cos20cos40cos60cos80
Multiply and divide with 2sin20
=2sin20cos20cos40cos60cos80/2sin20
We know that 2sinAcosA = sin 2A
So 2sin20cos20 = sin2*20 =sin40
= sin40cos40cos60cos80/2sin20
Multiply and divide with "2"
= 2sin40cos40cos60cos80/2*2sin20
=cos60sin80cos80/2*2sin20
Multiply and divide with "2"
= cos60*2sin80cos80/8sin20
= cos60sin160/8sin20
We know that
sin(180-∅) = sin∅
So sin160 = sin(180-20) = sin20
So,
= cos60sin160/8sin20
=cos60sin20/8sin20
= cos60/8
cos60 = 1/2
= 1/16
LHS = RHS
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