Question

联立方程的问题

Answer 1

a 3x-2y=-1 --- 1 4x+5y=14 --- 2 我们可以用消元法 1x4 : (3x-2y)x4=-1x4 = 12x-8y=＝-4－－－3 2x3 : (4x+5y)x3=14x3 = 12x+15y=42－－－4 3-4 : (12x-8y)-(12x+15y)=(-4)-(42) 23y = -46 y = -2－－－5 5代入3: 12x-8(-2)=＝-4 12x+16=-4 12x=12 x=1 b 2x-y=-7 ----1 3x+2=7 ----2 1x2: 4x-2y ＝ -14－－－3 3+2 : (4x--2y)+(3x+2y)=(-14)+(7) 7x = -7 x = -1 －－－4 4代入2: 3(-1)+2y = 7 -3+2y = 7 2y = 10 y = 5
参考: me自己计的
a 3x-2y=-1 --- 1 4x+5y=14 --- 2 1x4，12x-8y= -4-------3 2x3，12x+15y=42-----4 4-3 12x+15y-12x+8y=42+4 23y=46 y=2-----------5 5代入1 3x-2(2)= -1 x=1 所以x=1，y=2 b 2x-y=-7 ----1 3x+2=7 ----2 b果题唔知你系咪打少左个y(3x+2[y]=7 ----2) 所以我俾左两个答案你 b(1) 2x-y= -7 ----1 3x+2=7 ----2 由2，x=5/3--------3 3代入2， 2(5/3)-y= -7 10/3-y= -7 y=31/3---------4 所以x=5/3，y=31/3 b(2) 2x-y=-7 ----1 3x+2y=7 ----2 1x2，4x-2y= -14-------------3 2+3 3x+2y+4x-2y=7-14 7x=-7 x=-1-------------4 4代入1 2(-1)-y= -7 y=5 所以x=-1，y=5
a) 4x(1) 12x-8y=-4 -----(3) 3x(2) 12x+15y=42-----(4) (4)-(3) 23y=46 y=2 put y=2 into (3) 12x-16=-4 12x=12 x=1 b) 2x(1) 4x-2y=-14----(3) (2)+(3) 7x=-7 x=-1 put x=-1 into (1) 2(-1)-y=-7 -2+7=y y=5
a) 3x-2y=-1 2y = 3x + 1 y = 3x/2 + 1/2 Sub into 2 4x + 5(3x/2 + 1/2) = 14 11.5x + 2.5 = 14 x = 1 y = 3/2 + 1/2 = 2 b) 2x-y=-7 y = 2x + 7 Sub into 2 3x + 2(2x + 7) = 7 7x + 14 = 7 x = -1 y = 5