(1) 3x²+8x+1=0
(x²+2*4/3x+1/3)=0
(x²+2*4/3x+16/9 + 1/3-16/9)=0
(x+4/3)² = 13/9
x = -4/3 ± 1/3√13
(2) 2x²-7x+3=0
x²-7/2x+3/2=0
x²-2*7/4x+49/16+3/2-49/16=0
(x-7/4)² = 25/16
x = 7/4 ± 5/4 = 0.5 或 3
(3) -3x²+4x+1=0
x²-4/3x-1/3=0
x²-2*2/3x+4/9-1/3-4/9=0
(x-2/3)² = 7/9
x= 2/3 ± 1/3*√7
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