1.次の連立方程式を解け
{x=2y-4x+y=5
{5x-y=14y=7x-20
{x=-5y+152x+3y=2
{x=5y-42y=4x-3
{2x=-4y+62x+5y=10
{3x+4y=-174y=-5x-31
{7x=8y+32-7x+3y=-12
{3x-5y=-115y=x+7
①
{
x=2y-4…(1)
x+y=5…(2)
(1)を(2)に代入
(2y-4)+y=5
2y+y-4=5
3y = 5+4
3y = 9
y=3…(3)
(3)を(1)に代入
x = 2×3-4
x = 6-4
x=2
②
{5x-y=14…(1)y=7x-20…(2)
(2)を(1)に代入
5x-(7x-20) =14
5x-7x+20 = 14
-2x = 14-20
-2x = -6
x=3…(3)
(3)を(2)に代入
y=7×3-20
y=21-20
y=1
③
{x=-5y+15…(1)2x+3y=2…(2)
(1)を(2)に代入
2(-5y+15)+3y=2
-10y+30+3y=2
-7y = -28
y =4…(3)
(3)を(1)に代入
x=-5×4+15
x = -20+15
x=-5
④
{x=5y-42…(1)y=4x-3…(2)
(2)を(1)に代入
x=5(4x-3)-42
x=20x-15-42
-19x = -57
x=3…(3)
(3)を(2)に代入
y=4×3-3
y=12-3
y=9
⑤
{2x=-4y+6…(1)2x+5y=10…(2)
(1)を(2)に代入
-4y+6 +5y =10
y = 10-6
y = 4…(3)
(3)を(1)に代入
2x = -4×4+6
2x = -16+6
2x = -10
x=-5
⑥
{3x+4y=-17…(1)4y=-5x-31…(2)
(2)を(1)に代入
3x+(-5x-31)=-17
3x-5x = -17+31
-2x = 14
x =-7…(3)
(3)を(2)に代入
4y=-5×(-7)-31
4y =35-31
4y=4
y=1
⑦
{7x=8y+32…(1)-7x+3y=-12…(2)
(1)を(2)に代入
-(8y+32)+3y = -12
-8y-32+3y = -12
-5y = -12 +32
-5y = 20
y=-4…(3)
(3)を(1)に代入
7x = 8×(-4)+32
7x =-32+32 =0
x = 0
⑧
{3x-5y=-11…(1)5y=x+7…(2)
(2)を(1)に代入
3x-(x+7) = -11
3x-x-7 = -11
2x = -11 +7
2x = -4
x=-2…(3)
(3)を(2)に代入
5y = -2+7
5y=5
y=1
