a,3-4x(25x+2x)=8x^2+x-300
3-100x^2-8x^2=8x^2+x-300
-100x^2-8x^2-8x^2-x=-300-3
-116x^2-x =-303
-116x^2-x+303 = 0
b),2(1-3x)/5 - 2+3x/10=7-3(2x-1)/4
2-6x/5 - 2+3x/10 = 7- 6x+3/4
4(2-6x) - 2(2+3x) = 140 - 5(6x+3)
8-24x - 4-6x = 140-30x-15
-24x-6x+30x = 140-15-8+4
0x =121
=> PT vô nghiệm