X² + Y² = (X² + 2*X*Y + Y²) - 2*X*Y = (X + Y)² - 2*X*Y = 12² - 2*1 = 144 - 2 = 142
Х²-х-6<0
Парабола, ветви вверх
х²-х-6=0
Д=1+4*6=25
х₁=<u>1-5 </u>= -2
2
х₂=<u>1+5</u> =3
2
+ - +
--------- -2 ------------- 3 ---------------
\\\\\\\\\\\\\\
х∈(-2; 3)
Ответ: (-2; 3)
Решение смотри на фотографии
<span>(7a + 1)²</span><span> </span><span>- 28a</span>
<span>49a²+14a+1-28a</span>
<span>49a²-14a+1=0</span>
<span>a²-2/7a+1/49=0</span>
<span>a=1/7±√1/49-1/49</span>
<span>a=1/7</span>