请等一会
1.x2-2x+5-x2+3=-2x+8
2.x2+kx+16 x2+kx+16
=（x+4)^2 =（x-4)^2
所以k=4 所以k=-4
3.a*3my12/3x3y2n=4*6y8(不太明白,请加括号）
4..u应改成y
[(2x+y)2+2(x+y)(2x-u)+4xy]/2x.
=(4x^2+4xy+y^2+4x^2+2xy-2y^2+4xy)/2x
=(8x^2+10xy-y^2)/2x
=4x+5y-(y^2/2x)
5..3x2y/6xy+(15x2-5x)/(-10x).
=1-1.5x+0.5
=1.5-1.5x
6.(3x3n)2-4x(x2)2n
=81x^2n^2-8x^3n
=81*7n-8*7x
=567n-56x