oblicz rownanie metoda przeciwnych wspólczynnikow   a) x+y=1 2x+3y=7   b) x+2y=-8 -5y-2y=-2   c) 2x+5y=8 3x-2y=-7   d) 3x+7y=-1 5x-3y=13

a) x + y = 1 / * (-2) 2x + 3y = 7 -2x - 2y = -2 2x + 3y = 7 y = 5 x + 5 = 1 x = -4 y = 5 b) x + 2y = -8 -5x - 2y = -2 -4x = -10 / * (-4) x = 2,5 2,5 + 2y = -8 2y = -10.5 / /2 y= 5.25 x= 2,5 c) 2x+5y = 8 / * 3 3x - 2y = -7 / * (-2) 6x + 15y = 24 -6x+ 4y = 14 19y = 38 / 19 y = 2 2x + 5 *2 = 8 2x = -2 / /2 x = -1 y=2 d)  3x + 7y = -1 / * 5 5x - 3 y = 13 / * ( -3) 15x + 35y = -5 -15x +9y = -39 44y = -44 / /44 y = -1 3x + 7 *( -1) = -1 3x = 6 / 3 x = 2 y = 1