用因式分解法, 

(4)9(x-2)^2=4(x+1)^2
9x^2-36x+36=4x^2+8x+4
5x^2-44x+32=0
(5x-4)(x-8)=0
x=4/5, 8
(6)设x+2为y,得:
25y^2-30y+9=0
(5y)^2-2(5y)(3)+(3)^2=0
(5y-3)^2=0
y=3/5
代x+2,得:
x+2=3/5
x=-7/5