a) 2x-2y=7 4x+3y=21 2x=7+2y /:2 4x+3y=21 x=3,5+y 4(3,5+y)+3y=21 x=3,5+y 14+4y+3y=21 x=3,5+y 7y=21-14 x=3,5+y 7y=7/:7 x=3,5+y y=1 x=3,5+1 y=1 x=4,5 y=1 b) 0,4x+0,3y=1,4/*10 0,1x+3y=2,3/*10 4x+3y=14 x+30y=23 4x+3y=14 x=23-30y 4(23-30y)+3y=14 x=23-30y 92-120y+3y=14 x=23-30y -117y=14-92 x=23-30y -117y= -78/:(-117) x=23-30y y= 78/117 x=23-30*78/117 y=78/117 x=23- 20 y=78/117 x=3 c) 2x+3y=14 3x-2y=8 2x=14-3y/:2 3x-2y=8 x=7-1,5y 3(7-1,5y)-2y=8 x=7-1,5y 21- 4,5y-2y=8 x=7-1,5y -6,5y=8-21 x=7-1,5y -6,5y=-13/:(-6,5) x=7-1,5y y= 2 x=7-3 y=2 x=4 y=2 d) 1/2x-2y=8 2x+5y=6 1/2x=8+2y/*2 2x+5y=6 x =16+4y 2(16+4y)+5y=6 x=16+4y 32+8y+5y=6 x=16+4y 13y=6-32 x=16+4y 13y= -26/:13 x=16+4y y=-2 x=16-8 y=-2 x=8 y=-2 e) 1/2x-3/4y=0 2/3x+1 i 1/4y=9 1/2x=3/4y /*2 2/3x+1 1/4y=9 x=6/4y 2/3*6/4y+1 1/4y=9 x=6/4y 1y+1 1/4y=9 x=6/4y 2 1/4y=9/*4/9 x=6/4y y=4 x=6/4*4 y=4 x=6 y=4 f) 3x+4y= 1 i 2/3 6x+3y= 1 i 1/4 3x=5/3-4y /:3 6x+3y=1 1/4 x=5/9-4/3y 6(5/9-4/3y)+3y=1 1/4 x=5/9-4/3y 10/3-8y+3y=1 1/4 x=5/9-4/3y -5y=1 1/4-3 1/3 x=5/9-4/3y -5y=1 3/12-3 4/12 x=5/9-4/3y -5y=-2 1/12/:(-5) x=5/9-4/3y y=-25/12*(-1/5) x=5/9-4/3y y=5/12 x=5/9-4/3*5/12 y=5/12 x=5/9-5/9 y=5/12 x=0 y=5/12
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