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Trigonometry Compound Angles?
The value of cos5° * cos25° * cos40° + sin5° * sin25° * sin40° - sin20° * sin40° is
a) √3 / 2
b) 1 / 2
c) 1 / √2
d) - √3 / 2
2 Answers
- Kali PrasadLv 69 years agoFavorite Answer
above is in error.
I may be making a fool of my self
but if I change 1st sin 40 to cos 40
I get
cos5° * cos25° * cos40° + sin5° * sin25° * cos 40° - sin20° * sin40°
= cos40°( cos5° * cos25° + sin5° * sin25°) - sin20° * sin40°
= cos40° cos(25° - 5°) - sin20° * sin40°
= cos40° cos(20°) - sin20° * sin40°
= cos (40° + 20 °)
= cos 60°
= 1/2
is it what you wanted ?
- Anonymous4 years ago
cos 2?/9 cos 5?/18 - sin 2?/9 sin 5?/18= cos(2?/9 +5?/18)=cos(?/2)=0 cos 10?/9 cos 15?/18 + sin 10?/9 sin 5?/18 is this question as written terrific suited? sin (?/3 + ?/4)=sin(?/3)cos(?/4)+cos(?/3)sin(?/4)= sqrt(3) /2 sqrt(a million/2) + a million/2.sqrt(a million/2)
