若mn=a,1/m²+1/n²=b,则(m+n)²=?

mn=a,1/m²+1/n²=b
(1/m +1/n)² = 1/m² + 2/mn + 1/n² = b + 2/a
但是 (1/m+1/n)² = [(m+n)/mn]² = (m+n)² / m²n² = (m+n)²/a²
所以 b + 2/a = (m+n)²/a²
(m+n)² = a²b +2a

1/m²+1/n²=b 得到:(m²+n²)/m²n²=b, m²+n²=b*m²n²=b*a²
(m+n)²=m²+n²+2mn=a²b+2a

1/m²+1/n²=b得（n²+m²）/m²n²=b得n²+m²=b（mn）²=ba²
(m+n)²=n²+m²+2mn=ba²+2a