1-m^2+10mn-25n^2
=1－(m²－10mn＋25n²)
=1－(m－5n)²
=(1＋m－5n)(1－m＋5n)
x^3+3x^2-4x-12
=(x³＋3x²＋2x)－(6x＋12)
=x(x²＋3x＋2)－6(x＋2)
=x(x＋1)(x＋2)－6(x＋2)
=(x＋2)(x²＋x－6)
=(x＋2)(x＋3)(x－2)
x^2+2x-6y-9y^2
=(x²－9y²)＋(2x-6y)
=(x－3y)(x＋3y)＋2(x－3y)
=(x－3y)(x＋3y＋2)