Алгебра: Помогити пожалуйста !!!))))

A)
${87}^{2} - 174 \times 67 + {67}^{2} = \\ = {87}^{2} - 2 \times 87 \times 67 + {67}^{2} = \\ = ( {87 - 67})^{2} = {20}^{2} = 400$
b)
$\frac{ {38}^{2} - {17}^{2} }{ {47}^{2} - 361 } = \frac{ {38}^{2} - {17}^{2} }{ {47}^{2} - {19}^{2} } = \\ = \frac{(38 - 17)( 38 + 17)}{(47 - 19)(47 + 19)} = \\ = \frac{21 \times 55}{28 \times 66} = \frac{3 \times 5}{4 \times 6} = \frac{5}{4 \times 2} = \frac{5}{8}$