初一下平方差公式计算(过程详细)(1).(3x+7y)(3x-7y0(2).(0.2x-0.3)(0.2x+0.3)(3).(mn-3n)(mn+3n)(4).(-2x+3y)(-2x-3y)(5).(-1/4x-2y)(-1/4x+2y)(6).x^2+(y-x)(y+x)(7).(a^n+b)(a^n-b)(8).(a+1)(a-1)(a^2+1)1).(3x+7y)(3x-7y)

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

9x^2-49y^2\0.04x^-0.09\m^2n^2-9n^2\4x^2-9y^2\1/16x^2-4y^2\y^2\a^2n-b^2\a^4-1...这些都是用a^2-b^2=(a+b)(a-b) 这个公式啊

(1).(3x+7y)(3x-7y)=9x^2-49y^2
(2).(0.2x-0.3)(0.2x+0.3)= 0.04x^2-0.09
(3).(mn-3n)(mn+3n)=(mn)^2-9n^2
(4).(-2x+3y)(-2x-3y)=4x^2-9y^2
(5).(-1/4x-2y)(-1/4x+2y)=1/16x^(-2)-4y^2
(6).x^2+(y-x)(y+x)=y^2
(7).(a^n+b)(a^n-b)=a^2n-b^2
(8).(a+1)(a-1)(a^2+1)=a^4-1
以上均利用平方差公式a^2-b^2=(a+b)(a-b);

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

(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...