(a+b)(a-b)=a^2-b^2 例：(5+2)乘（5-2）=5^2-2^2.(a+b)^2=a^2+2ab+b^2.(a-b)^2=a^2-2ab+b^2.(-a-b)^2=a^2+2ab+b^2.(-a+b)^2=a^2-2ab+b^2.例:(5+2)=5^2+20+2^2.(-5-2)=5^2+20+2^2.(5-2)=5^2-20+2^2.(-5+2)=5^2-20+2^2...