唔好意思._.數學3題(20點)急

Identities used :
(u ± v)² = u² ± 2uv + v²


1.
[a + (1/3)]²
= (a)² + 2(a)(1/3) + (1/3)²
= a² + (2a/3) + (1/9)


2.
(1 - 6mn)²
= (1)² - 2(1)(6mn) + (6mn)²
= 1 - 12mn + 36m²n²


3.
[(m/2) + (n/3)]²
= (m/2)² + 2(m/2)(n/3) + (n/3)²
= (m²/4) + (mn/3) + (n²/9)