(a+2b)的平方=a^2+4ab+4b^2=a^2+4b^2+4n=m
a^2+4b^2=m-4n
(1/2a-b)^2=1/4a^2-ab+b^2=(a^2+4b^2-4ab)/4=(a^2+4b^2-4n)/4
代人得:(1/2a-b)^2 =(m-4n-4n)/4
=(m-8n/4)
(a+2b)的平方=a^2+4ab+4b^2=a^2+4b^2+4n=m
a^2+4b^2=m-4n
(1/2a-b)^2=1/4a^2-ab+b^2=(a^2+4b^2-4ab)/4=(a^2+4b^2-4n)/4
代人得:(1/2a-b)^2 =(m-4n-4n)/4
=(m-8n/4)