Question

初二数学，求解答，急

Answer 1

（1）4x3+4x2y-9xy2-9y3
=4x2(x+y)-9y2(x+y)
=(x+y)(4x2 -9y2)
=(x+y)(2x+3y)(2x-3y)

（2）x3y-3x2-2x2y2+6xy
=x2(y-3)-2xy(y-3)
=(y-3)(x2-2xy)
=x(y-3)(x-2y)

(3)4a2-b2+6a-3b
=(2a+b)(2a-b)+3(2a-b)
=(2a-b)(2a+b+3)

(4)9m2-6m+2n-n2
=9m2-n2-6m+2n
=(3m+n)(3m-n)-2(3m-2)
=(3m-2)(3m+n-2)
希望采纳

Answer 2

过D作DE⊥AB，DF⊥BC，垂足分别为E，F
由角平分线可知DE=DF
又由AD=DC可知Rt△ADE≌CDF
所以∠C=∠DAE
由∠DAE+∠DAB=180°可知∠C+∠DAB=180°
即∠A+∠C=180°