=1/2*(x^2+2xy+y^2)=1/2*[(x+y)^2】=1/2*1=1/2
25^7=5^145^14-5^12=5^12(25-1)=5^11x5x241/2(x^2+y^2)=1/2[(x+y)^2-2xy]=1/2-xy所以，此等试的值为1/2
