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B) 唔明阿~
-[]-[]-[]-[]-一一一一條MATHS~
2007-07-12 8:46 am
回答 (2)
2007-07-12 9:10 am
第一個紅色正方形
因為 cos(90 -x) = sin x
所以 [cos(90-x)]^2 = sinx cos(90-x)
而且因為1/[tan (90 -x )] = tan x
所以 [cos(90-x)]^2 /[sin x sin (90-x)] = sinx cos(90-x)/ [sin x sin (90-x)]
= 1/[tan (90 -x )] = tan x
第二個紅色正方形
我估佢係given 左 0<90
所以劃返個直角三角形, 對邊係 4, 鄰邊係 3, 斜邊就係 sqrt(3^2+4^2) = 5
cos x = 鄰邊/ 斜邊 = 3/5, sin x = 對邊/ 斜邊 = 4/5
sin x + cos x = 3/5 +4/5 = 7/5
因為 cos(90 -x) = sin x
所以 [cos(90-x)]^2 = sinx cos(90-x)
而且因為1/[tan (90 -x )] = tan x
所以 [cos(90-x)]^2 /[sin x sin (90-x)] = sinx cos(90-x)/ [sin x sin (90-x)]
= 1/[tan (90 -x )] = tan x
第二個紅色正方形
我估佢係given 左 0<90
所以劃返個直角三角形, 對邊係 4, 鄰邊係 3, 斜邊就係 sqrt(3^2+4^2) = 5
cos x = 鄰邊/ 斜邊 = 3/5, sin x = 對邊/ 斜邊 = 4/5
sin x + cos x = 3/5 +4/5 = 7/5
收錄日期: 2021-04-13 14:31:47
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070712000051KK00181