设x+y=6,x-y=5,则x^2-y^2=

x^2-y^2=(x+y)(x-y)=6*5=30

x^2-y^2=(x-y)(x+y)=30

x+y=6,x-y=5,的方程组的解为
x=11/2,y=1/2
所以x^2-y^2=121/4-1/4=30

x^2-y^2=(x+y)*(x-y)=6*5=30
平方差公式。

也可以由x+y=6和x-y=5算得x=11/2,y=1/2. 则x^2-y^2=121/4-1/4=120/4=30

x+y=6 <1>
x-y=5 <2>
<1>+<2>
x=11/2
y=1/2
x^2-y^2
=121/4-1/4
=120/4
=30