Grade 11Trigonometry
2(Cos2 73o +cos247o)-154o it seems very hard please help me
2(Cos2 73o +cos247o)-154o
it seems very hard please help me
1 Answer
somi teez
Hi,
i will help..take ease....please go through each step
so,
let A=73 degree and B=47 degree
we find that , 154=180-(73-47) in terms of degree
Expression is now,
=2( cos^2 A + cos^2 B ) - cos [ pi - (A - B) ]
= 2cos^2A +2cos^2B + cos(A - B) [ using cos (pi-X) = - cosX ]
So,
So,
=2cos^2A +2cos^2B + cos(A - B)
= (2 cos^2A - 1) + (2 cos^2B - 1) + cos(A - B) +2
= cos 2A + cos 2B + cos(A - B) +2
= cos146 + cos94 + cos26 +2
Now,
= cos 2A + cos 2B + cos(A - B) +2
= cos146 + cos94 + cos26 +2
Now,
=[cos 146 + cos 94 ] = 2cos120 * cos26 { cosC+cosD = 2cos(C+D)/2*cos(C-D)/2 }
So now expression,
So now expression,
= 2cos120 * cos26 + cos26 + 2
= 2(-1/2)*cos26+cos26+2 we know cos 120 = - cos 60 = -1/2
= -cos26+cos26+2 = 2.
= 2(-1/2)*cos26+cos26+2 we know cos 120 = - cos 60 = -1/2
= -cos26+cos26+2 = 2.
i hope you understand...just go with the formulas
approve it if you agree
BEST OF LUCK!!!!
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