[tex](a - b) ^{2} = a^{2} - 2ab + b ^{2} [/tex]
te folosesti de formula asta
[tex]( \frac{1}{2} x - y) ^{2} = ( \frac{1}{2} x) ^{2} - 2 \times \frac{1}{2} x \times ( - y) + y ^{2} = \frac{1}{4} x^{2} + x \times y + y ^{2} = [/tex]
sper ca te am ajutat
