x^2-81=x^2-9^2=(x+9)*(x-9)
1/4 a^2-b^2=(1/2 a)^2-b^2=(1/2 a+b)(1/2 a-b)
9(x-y)^2-25=[3(x-y)]^2-5^2=(3x-3y+5)(3x-3y-5)
数学公因式法告诉我第一题的8个小题,关键、重点是要你们写出过程,我特别想看过程!
x^2-81=x^2-9^2=(x+9)*(x-9)
1/4 a^2-b^2=(1/2 a)^2-b^2=(1/2 a+b)(1/2 a-b)
9(x-y)^2-25=[3(x-y)]^2-5^2=(3x-3y+5)(3x-3y-5)