Question

x la a doua- y la a doua=16 si x+y=8, calculați 2x-2y

Answer 1

$x + y = 8$

${x}^{2} - {y}^{2} = 16$

${x}^{2} - {y}^{2} = (x -y )(x + y)$

$(x - y)(x + y) = 16$

$(x - y) \times 8 = 16 \: | \div 8$

$x - y = 2 \: | \times 2$

$2x - 2y = 4$