(a-b)²=(a-b)×(a-b)=a×a-a×b-b×a-b×(-b)=a²-ab-ba+b² =a²-ab-ab+b² =a²-2ab+b²
追问已知a²±2ab+b²,求(a+b)²要求写过程!!!
追答用十字相乘,知道不??
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/ae51f3deb48f8c5412c4fdd03a292df5e0fe7f3d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
多项式中第一项和最后一项拆开来,竖着写,即a×a=a²,b×b=b²,交叉相乘再相加等于中间一项,即a×b+a×b=2ab,最后结论就是第一行相加乘以第二行相加,即(a+b)²,所以a²+2ab+b²=(a+b)²
如果是a²-2ab+b² 就是
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/b8014a90f603738d515937ddb31bb051f819ec3a?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
不知道你看得懂不?
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