標題:
maths 1
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發問:
x+y=20 2x+y=50 更新: 求x和y
最佳解答:
this is Q of 2 equations of 2 unknowns Method 1 : By elimination :x+y=20------(1) 2x+y=50 -----(2) You can observe that the y can be cancelled by (2) minus (1), it becomes a linear equation in 1 unknown (x only) (2)--(1): 2x-x=50--20 x=30 Put x=30 to (1) Reason : (1) is more simple than (2) y=20-x=20-30=-10 Method 2 :By substitution : For both 1 and 2 , express y in terms of x : y=20-x y=50-2x Equate them together : 20-x=50-2x x=30 and y=20-30 or 50-2(30)=-10
其他解答:
x+y=20------------(1) 2x+y=50----------(2) (2)-(1), 2x+y-(x+y)=50-20, 2x+y-x-y=30, 2x-x+y-y=30, x=30 將 x 代入 (1), 30+y=20, y=-10 Answer, x=30, y=-10|||||x+y=20 x=20-y 2x+y=50 2(20-y)+y=50 40-y=50 y= -10 x+y=20 x-10=20 x=30|||||x+y=20 x=20-y 2x+y=50 2(20-y)+y=50 40-y=50 y= -10 x+y=20 x-10=20 x=30|||||x+y=20............1 2x+y=50..........2 1-2 x+Y-2X-Y=20-50 -X=-30 X=30 30+Y=20 Y=-10|||||x+y=20 -(1) 2x+y=50 -(2) (2) - (1): (2x-x) + (y-y) = (50-20) x =30 in (1) 30 + y =20 so y = -10 Checked the results in (2) 2 * 30 + (-10) = 50 Answers: x = 30 y = -10
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