Câu hỏi
b. Giải phương trình: 4x^2+14x+11=4sqrt (6x+10)
Giải pháp
4.2
(136 Phiếu)
Bùi Hiếu Tín
thầy · Hướng dẫn 5 năm
Trả lời
Let the equation be
4x^2 + 14x + 11 = 4\sqrt{6x+10}
Let
. Then
, so
. Substituting into the original equation:
4x^2 + 14x + 11 = 4u
4x^2 + 14x + 11 - 4u = 0
From
,
. Substituting this into the equation above:
4\left(\frac{u^2 - 10}{6}\right)^2 + 14\left(\frac{u^2 - 10}{6}\right) + 11 - 4u = 0
4(u^4 - 20u^2 + 100) + 84(u^2 - 10) + 396 - 144u = 0
4u^4 - 80u^2 + 400 + 84u^2 - 840 + 396 - 144u = 0
4u^4 + 4u^2 - 144u - 44 = 0
u^4 + u^2 - 36u - 11 = 0
This quartic equation is difficult to solve analytically. Numerical methods are required to find the roots for *u*, and then solve for *x*. A numerical solver yields approximate solutions for u, which can then be used to find x. There is no simple analytical solution.