Quick math question

cos(x+y)=cosxcosy-sinxsiny
cos(x-y)=cosxcosy+sinxsiny

2006-12-30 07:19:18 補充：
sin(-x) = -sin(x)csc(-x) = -csc(x)cos(-x) = cos(x)sec(-x) = sec(x)tan(-x) = -tan(x)cot(-x) = -cot(x) sin^2(x) + cos^2(x) = 1 tan^2(x) + 1 = sec^2(x) cot^2(x) + 1 = csc^2(x)

2006-12-30 07:19:58 補充：
sin(x+y) = sin x cos y + cos x sin y sin(x-y) = sin x cos y - cos x sin y cos(x+y) = cos x cosy - sin x sin y cos(x-y) = cos x cosy + sin x sin y tan(x+y) = (tan x + tan y) / (1- tan x tan y) tan(x-y) = (tan x - tan y) / (1+ tan x tan y)

2006-12-30 07:20:28 補充：
sin(2x) = 2 sin x cos x cos(2x) = cos^2(x) - sin^2(x) = 2 cos^2(x) - 1 = 1 - 2 sin^2(x) tan(2x) = 2 tan(x) / (1 - tan^2(x)) sin^2(x) = 1/2 - 1/2 cos(2x) cos^2(x) = 1/2 + 1/2 cos(2x)

cos(x+y)=cosxcosy-sinxsiny

cos(x-y)=cosxcosy+sinxsiny