a)5x-y=7 2(x-1)=2y y=5x+7 2(x-1)=2(5x+7) 2x-2=10x+14 2x-10x=14+2 -8x=16/:(-8) -x=-2 x= 2 y=17 b) 4(x-2)-y=1 2x-4y=8 4x-8-y=1 2x-4y=8 4x-8-1=y 2x-4(4x-8-1)=8 2x-16x+32+4=8 2x-16x=8-32-4 -14x=-28 x=2 y= - 1 c) a/3 + b/5=7 / ×15 a/4- b/5=0 / × 20 5a+3b=105 5a-4b=0 5a=105-3b 105-4b-3b=0 -7b=105 / :(-7) b= 15 5a+3×15=105 5a+45=105 5a=60 a=12 b=15 d) k/3 + l/4=1 / ×12 k/4+ l/8=1 / ×8 4k + 3l = 12 2k + l = 8 4k+3l=12 l=8-2k 4k+3(8-2k)=12 4k+24-6k=12 4k-6k=12-24 -2k=-12 k=6 l= - 4
a)5x-y=7 2(x-1)=2 -y=7-5x/*(-1) 2x-2=2 y=-7+5x 2x=2+2 y=-7+5x 2x=4/:2 y=-7+5x x=2 y=-7+5*2 x=2 y=-7+10 x=2 y=3 x=2 b)4(x-2)-y=1 2x-4y=8 4x-8-y=1 2x-4y=8 4x-y=1+8 2x-4y=8 4x-y=9/*(-4) 2x-4y=8 -16x+4y=-36 2x-4y=8 -14x=-28/:(-14) x=2 2x-4y=8 x=2 2*2-4y=8 x=2 4-4y=8 x=2 -4y=8-4 x=2 -4y=4/:(-4) x=2 y=-1 x=2
