7x2+7x=√1/28(4x+9)
7x2+7x=(√4x+9)/(2√7)
7x(x+1)=(√4x+9)/(2√7)
√4x+9=14√7x2+14√7x
(√7)√4x+9=98x(x+1)
x=5/(7√2)−3/7hoặcx=−4/7−(√23/2)/7