1.9(a²-b²)+12(a²+b²) 2.（x²-2x）²+2x²-4x+13.49（x-y）²-25（x+y）² 4.81x的五次方y的五次方-16xy 5.（x²-5x）²-36
问题描述：
1.9(a²-b²)+12(a²+b²) 2.（x²-2x）²+2x²-4x+1
3.49（x-y）²-25（x+y）² 4.81x的五次方y的五次方-16xy 5.（x²-5x）²-36
答
1.9(a²-b²)+12(a²+b²) =9a²-9b²+12a²+12b²=21a²+3b²
2. （x²-2x）²+2x²-4x+1=(x²-2x)²+2(x²-2x)+1=(x²-2x+1)²=(x-1)^4
49（x-y）²-25（x+y）² =[7(x-y)+5(x+y)][7(x-y)-5(x+y)]
=(7x-7y+5x+5y)(7x-7y-5x-5y)
=(12x-2y)(2x-12y)
=4(6x-y)(x-6y)
4. 81x^5y^5-16xy =xy(81x^4y^4-16)
=xy(9x²y²+4)(9x²y²-4)
=xy(9x²y²+4)(3xy+2)(3xy-2)
5. （x²-5x）²-36=(x²-5x+6)(x²-5x-6)=(x-2)(x-3)(x-6)(x+1)
答
1.9(a²-b²)+12(a²+b²) ＝9a²－9b²＋12a²＋12b²＝21a²－3b²＝3﹙7a²－b²﹚;2.（x²-2x）²+2x²-4x+1＝﹙x－1﹚^4;3.49（x-y）²-25（...