∴(36x^2+84x+49)(3x^2+7x+4)=6，

Let y = 3x 2+7x+4, then

( 12y+ 1)y=6，

12y^2+y-6=0，

Y=2/3 or -3/4,

That is 3x 2+7x+4 = 2/3, or 3x 2+7x+4 =-3/4,

Arrange 3x 2+7x+ 10/3 = 0 or 3x 2+7x+ 19/4 = 0,

The solution is x 1 =-2/3, x2 =-5/3, x3 = (-7+2 √ 2i)/6, x4 = (-7-2 √ 2i)/6.