Question

Решить систему уравнений:
${x}^{2} - {y}^{2} = 21 \\ x - y = 3$
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Answer 1

$\displaystyle\bf\\\left \{ {{x^{2} -y^{2} =21} \atop {x-y=3}} \right. \\\\\\\left \{ {{(x-y)(x+y)=21} \atop {x-y=3}} \right. \\\\\\\left \{ {{3\cdot(x+y)=21} \atop {x-y=3}} \right.\\\\\\+\left \{ {{x+y=7 \atop {x-y=3}} \right. \\--------\\2x=10\\\\x=5\\\\y=7-x=7-5=2\\\\Otvet:(5 \ ; \ 2)$