А)2х. 7х²
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х-у х²-у²


Б) 3а-6ав. 2а²в
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а⁴в³ 1-4в²

12x/(x-y)+7x²/(x-y)(x+y)=(2x²+2xy+7x²)/9x²-y²)=(9x²+2xy)/9x²-y²)23a(1-2b)/a^4b³ *2a²b/(1-2b)(1+2b)=6/ab²(1+2b)