初一下平方差公式计算(过程详细)

(1).(3x+7y)(3x-7y)
=(3x)^2-(7y)^2
=9x^2-49y^2
(2).(0.2x-0.3)(0.2x+0.3)
=(0.2x)^2-0.3^2
=0.04x^2-0.09
(3).(mn-3n)(mn+3n)
=(mn)^2-(3n)^2
=m^2n^2-9n^2
(4).(-2x+3y)(-2x-3y)
=(-2x)^2-(3y)^2
=4x^2-9y^2
(5).(-1/4x-2y)(-1/4x+2y)
=(-1/4x)^2-(2y)^2
=1/16x^2-4y^2
(6).x^2+(y-x)(y+x)
=x^2+(y^2-x^2)
=y^2
(7).(a^n+b)(a^n-b)
=(a^n)^2-b^2
=a^2n-n^2
(8).(a+1)(a-1)(a^2+1)
=(a^2-1)(a^2+1)
=a^4-1