(2) AD/AC=sin30/sin130=1/2*1/sin130
sin130*sin40/sin80=1/2*(cos(130-40)-cos(130+40))/sin80=1/2*(cos90-cos170)/sin80=1/2*(0-cos(90+80))/sin80=1/2*sin80/sin80=1/2
=>1/2*1/sin130=sin40/sin80
=>(1)=(2)
...
(2) AD/AC=sin30/sin130=1/2*1/sin130
sin130*sin40/sin80=1/2*(cos(130-40)-cos(130+40))/sin80=1/2*(cos90-cos170)/sin80=1/2*(0-cos(90+80))/sin80=1/2*sin80/sin80=1/2
=>1/2*1/sin130=sin40/sin80
=>(1)=(2)
...
•
或者,直接利用三角公式列方程求出X :)
-网恋无罪-
♂
(411 bytes)
()
11/16/2011 postreply
15:39:41
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要求不用三角公式而用初等几何的方法解题.
-redplum-
♀
(131 bytes)
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11/16/2011 postreply
19:27:35