Решебник по алгебре 7 класс Мерзляк ФГОС Задание 659

 

\[\boxed{\text{659\ (659).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[a + b = 7;\ \ ab = 2\]

\[a^{2} + b^{2} =\]

\[= \left( a^{2} + 2\text{ab} + b^{2} \right) - 2\text{ab} =\]

\[= (a + b)^{2} - 2\text{ab} = 7^{2} - 2 \cdot 2 =\]

\[= 49 - 4 = 45\]

\[Ответ:45.\]

\[\boxed{\text{659.\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[x^{2} - y^{2} = (x - y)(x + y)\]

\[1)\ x = 75;y = 25\]

\[(75 - 25)(75 + 25) =\]

\[= 50 \cdot 100 = 5000\]

\[2)\ x = 10,5;y = 9,5\]

\[(10,5 - 9,5)(10,5 + 9,5) =\]

\[= 1 \cdot 20 = 20\]

\[3)\ x = 5,89;y = 4,11\]

\[(5,89 - 4,11)(5,89 + 4,11) =\]

\[= 1,78 \cdot 10 = 17,8\]

\[4)\ x = 3,04;\ \ y = 1,96\]

\[(3,04 - 1,96)(3,04 + 1,96) =\]

\[= 1,08 \cdot 5 = 5,4.\]