Đáp án:
$\\$
`15/4 + 2 (x-2/5)^2 = 393/25`
`-> 2 (x-2/5)^2= 393/25 - 15/4`
`-> 2 (x-2/5)^2 = 1572/100 - 375/100`
`-> 2 (x-2/5)^2 = 1197/100`
`-> (x-2/5)^2 = 1197/100 ÷2`
`-> (x-2/5)^2 = 1197/200`
Trường hợp 1 :
`-> (x-2/5)^2 = (\sqrt{1197/200})^2`
`-> x-2/5 = \sqrt{1197/200}`
`-> x= \sqrt{1197/200} + 2/5`
`-> x =(8 + 3 \sqrt{266})/20`
Trường hợp 2 :
`-> (x-2/5)^2 = (-\sqrt{1197/200})^2`
`-> x-2/5 = -\sqrt{1197/200}`
`-> x = -\sqrt{1197/200} + 2/5`
`->x = (8-3\sqrt{266})/20`
Vậy `x=(8 + 3 \sqrt{266})/20` hoặc `x = (8-3\sqrt{266})/20`
