What is the the exact value of cos124°cos56°-sin124°sin56° without a calculator?
Can someone help me out with this pre-calc question?
2006-12-02 02:16:48 · 3 answers · asked by x_abbie_2006_x 1 in Science & Mathematics ➔ Mathematics
Use the fact that
cos(a)cos(b) - sin(a)sin(b) = cos(a+b)
With a = 124 and b = 56,
cos124°cos56°-sin124°sin56° = cos(124 + 56)
= cos(180) (which is the same as taking cos (pi) )
cos(pi) = -1
2006-12-02 02:19:16 · answer #1 · answered by Puggy 7 · 1⤊ 0⤋
cos 124 is -cos((180-124) so that part is -cos(56)cos(56) and the other bit ( using the same sort of moves ) is -sin(56)sin(56) and as far as I can tell you get -1*(cos^2+sin^2) = -1
2006-12-02 10:31:38 · answer #2 · answered by Anonymous · 0⤊ 0⤋
well because most of the tricky questions people ask end up being either 1 or 0, so one of those.. if the answer was like 391 or some random question no one would ask it =)
2006-12-02 10:26:34 · answer #3 · answered by Anonymous · 0⤊ 0⤋