Question

Решите плиз!!! Даю 20 баллов​

Answer 1

$\dfrac{d+7}{(7-d)^2}+\dfrac{7}{7d-d^2}=\dfrac{d+7}{(7-d)^2}+\dfrac{7}{d\, (7-d)}=\dfrac{d\, (d+7)+7\, (7-d)}{d\, (7-d)^2}=\\\\\\=\dfrac{d^2+7d+49-7d}{d\, (7-d)^2}=\dfrac{d^2+49}{d\, (7-d)^2}$