12. b) 2x - 3/4 = 1/2 + x/•4
6x - 12 = 2 + 4x/-4x
2x - 12 = 2/+12
2x = 14/:2
x= 7
f) x/2 = 2/5(4-x)-4
x/2 = 8/5 - 2/5x - 4
x/2 = 12/5 - 2/5x
5x = -24 - 4x
9x = -24
x = -8/3
13. b) (x-4)(x+5)-x2=3
x2 + 5x -4x -20 -x2 = 3
x - 20= 3/+20
x = 23
f) (x-3)(4x+2)=4x2+3
4x2+2x-12x-6=4x2+3
4x2-10x-6=4x2+3/-4x2
-10x -6=3/+6
-10x=9/:10
x=-0,9
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