Question

(-x-7)(x-7)+x(x+14) при x=-3/7​

Answer 1

Ответ:

$x=-\dfrac{3}{7}\\\\\underbrace{(-x-7)}_{-(x+7)}(x-7)+x(x+14)=-\underbrace {(x+7)(x-7)}_{x^2-7^2}+x(x+14)=\\\\=-(x^2-49)+x^2+14x=-x^2+49+x^2+14x=49+14x=\\\\=7\, (7+2x)=7\cdot \Big(7-2\cdot \dfrac{3}{7}\Big)=7\cdot \Big(7-\dfrac{6}{7}\Big)=7\cdot \dfrac{7\cdot 7-6}{7}=7\cdot \dfrac{43}{7}=43$