çæ¡æ¯12
设Oç¹å°ADçåç´è·ç¦»ä¸ºh1, åä¸è§å½¢AODçé¢ç§¯= 1/2 * AD *h1
设Oç¹å°BCçåç´è·ç¦»ä¸ºh2, åä¸è§å½¢BOCçé¢ç§¯= 1/2 * BC *h2
Eæ¯OCçä¸ç¹,æ以ä¸è§å½¢BOEçé¢ç§¯æ¯ä¸è§å½¢BOCçé¢ç§¯ç1/2 = 1/2 *ï¼1/2 * BC *h2ï¼
ä¸è§å½¢AODçé¢ç§¯ä¸ä¸è§å½¢BOEçé¢ç§¯ä¹åæ¯4ï¼ä¹å°±æ¯
1/2 * AD *h1 + 1/2 *ï¼1/2 * BC *h2ï¼= 4 èä¸BC=2ADï¼å¸¦å
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1/2 * AD *h1 + 1/4 * 2AD * h2 =4
1/2 * AD * (h1+h2) = 4
h1 +h2 æ£å¥½æ¯æ¢¯å½¢çé«çè·ç¦»ï¼è®¾ä¸ºh,ä¸è¾¹çå¼å为 1/2 * AD * h = 4
=====> AD*h=8
梯形ABCDé¢ç§¯= 1/2 * (AD+BC)*h=1/2 * (AD+2AD)*h=1/2 * 3AD*h=1/2 * 3* 8= 12
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