Diketahui sistem persamaan linear dua variabel 1/4× - 1/2y + 1 =0 dan 1/2× + 1/4y + 3/4 =0 maka nilai dari 3x+7y adalah ....

1/4x - 1/2y = -1 ---------------- p(1)
1/2x + 1/4y = -3/4 ------------- p(2)

*eliminasi p(1) & p(2)
1/4x - 1/2y = -1 | (×1)
1/2x + 1/4y = -3/4 | (×1/2)
=》1/4x - 1/2y = -1
=》1/4x + 1/8y = -3/8
________________ (-)
-5/8y = -3/8
y = 3/8 . 8/5
y = 3/5

*subsitusi y=3/5 ke p(1)
1/4x - 1/2y = -1
1/4x - 1/2(3/5) = -1
1/4x - 3/10 = -1
1/4x = -1 + 3/10
1/4x = -7/10
x = -7/10 . 1/4
x = -7/40


jadi,
x = -7/40
y = 3/5