想請問下以下題目點做
28(X+Y)^2-7(X-Y)^2
請清楚列出步驟
希望大家幫下手啦
最佳回答取４０分：數學題一條
2007-09-06 3:13 am
回答 (8)
2007-09-06 3:16 am
✔ 最佳答案
28(X+Y)^2-7(X-Y)^2=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
2007-09-06 3:41 pm
28(X+Y)^2-7(X-Y)^2
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2-(X-Y)^2}
=7[2(X+Y)+(X-Y)][2(X+Y)-(X-Y)]
=7(2X+2Y+X-Y)(2X+2Y-X+Y)
=7(3X+Y)(X+3Y)
Therefore, 28(X+Y)^2-7(X-Y)^2=7(3X+Y)(X+3Y)
(Also can writing 7(3X+Y)(X+3Y)=7(3X^2+9XY+YX+3Y^2)=7(3X^2+10XY+3Y^2)=21X^2+70XY+21Y^2 )
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2-(X-Y)^2}
=7[2(X+Y)+(X-Y)][2(X+Y)-(X-Y)]
=7(2X+2Y+X-Y)(2X+2Y-X+Y)
=7(3X+Y)(X+3Y)
Therefore, 28(X+Y)^2-7(X-Y)^2=7(3X+Y)(X+3Y)
(Also can writing 7(3X+Y)(X+3Y)=7(3X^2+9XY+YX+3Y^2)=7(3X^2+10XY+3Y^2)=21X^2+70XY+21Y^2 )
2007-09-06 3:57 am
28(X+Y)^2-7(X-Y)^2
=7[4(X+Y)^2-(X-Y)^2]
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(2X-X+2Y+Y)(2X+X+2Y-Y)
=7(X+3Y)(3X+Y)
=7[4(X+Y)^2-(X-Y)^2]
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(2X-X+2Y+Y)(2X+X+2Y-Y)
=7(X+3Y)(3X+Y)
參考: 自己
2007-09-06 3:29 am
28(X+Y)^2-7(X-Y)^2
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
2007-09-06 3:28 am
28(X+Y)^2-7(X-Y)^2
=28 (X^2+2XY+Y^2) - 7 (X^2-2XY+Y^2)
=28X^2 + 56XY + 28Y^2 - 7X^2 +14XY - 7Y^2
=21X^2 + 70XY + 21Y^2
=7 (3X^2 +10XY + 3Y^2)
=7(3X+Y)(X+3Y)
=28 (X^2+2XY+Y^2) - 7 (X^2-2XY+Y^2)
=28X^2 + 56XY + 28Y^2 - 7X^2 +14XY - 7Y^2
=21X^2 + 70XY + 21Y^2
=7 (3X^2 +10XY + 3Y^2)
=7(3X+Y)(X+3Y)
2007-09-06 3:25 am
28(X+Y)^2-7(X-Y)^2
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
2007-09-06 3:24 am
28(X+Y)^2-7(X-Y)^2
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)#
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)#
參考: 自己
2007-09-06 3:21 am
28(X+Y)^2-7(X-Y)^2
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
=7[4(X+Y)^2-(X-Y)^2]
=7{[2(X+Y)]^2--(X-Y)^2}
=7(2X+2Y-X+Y)(2X+2Y+X-Y)
=7(X+3Y)(3X+Y)//
參考: 個人
收錄日期: 2021-04-13 13:20:17
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070905000051KK03218