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Persamaan Linier Dua Variabel

x + 4y =  - 5
2x - y =  10
..
a) dengan cara substitusi
x + 4y = - 5
x= - 4y - 5 .... sub ke  2x - y = 10
2(-4y - 5) - y = 10
-8y - 10 - y = 10
-9y = 10 + 10
-9y = 20
y = - 20/9 --> sub ke x = - 4y - 5
x = - 4( -20/9) - 5
x = 80/9 - 5
x = 80/9 - 45/9
x = 35/9
hp (x,y) = (35/9, - 20/9)

b) cara eliminasi
x + 4y = -5 .....||kalikan2
2x - y = 10....||kalikan 1
..
2x + 8y = -10
2x - y = 10
......(-).......
9y = - 20
y = -20/9
..

x + 4y = -5 .....|kalikan 1
2x - y = 10......|kalikan 4
..
x + 4y = - 5
8x - 4y = 40
.........(+).....
9x = 35
x = 35/9

HP (x,y) = ( 35/9 , -20/9)