初2因式分解

①6x^2y(x-y)^3-4xy^2(y-x)^3
=6x^2y(x-y)^3+4xy^2(x-y)^3
=2xy(x-y)^3(3x+2y)
②x^4-18x^2+81
=(x^2-9)^2
=(x+3)^2(x-3)^2
若x^2-kx+25是一个完全平方式，则为（x±5）^2
故k=±10

①原式=6X^2Y*(X-Y)^3+4XY^2(X-Y)^3
=2XY(3X+2Y)(X-Y)^3
②原式=x^4-18x^2+81
=(X^2-9)^2
=(X-3)^2(X+3)^2
第三问:x^2-kx+25=x^2-kx+5^2
所以平方项应为-K=2*±5
K=±10