Răspuns :
[tex]a) {x}^{7} : x ^{4}:x = {x}^{7 - 4-1}={x}^{2} ≠ {x}^{3} \:=> F \\ \\ b) A \\ \\ c)x = 10 - 2y \\ \\ [2(10 - 2y) + 6y] ^{2} = 100 \\ \\ (20 - 4y + 6y) ^{2} = 100 \\ \\ (2y + 20) ^{2} = 100 \\ \\ {4y}^{2} + 80y + 400 ≠ 100 \:=> F[/tex]