int(du/sqrt(u))=(1/7)*int(dx/x)
u^(1/2)/(1/2) = (1/7) * ln |x| + C
2 * u^(1/2) = 1/7 * ln |x| + C
2 * (y/x)^(1/2) = 1/7 * ln |x| + C
Вот и ответ.