Soal umpn 2017 matematika no 28, ,29,30

28) (p ... q) (x) = (p)
...... (q ... p) (y) ... (q)
px + qy = p
qx + py = q
---------------- +
px + qx + qy + py = p + q
(p + q)x + (p + q)y = (p + q) ======> kedua ruas dibagi (p + q)
x + y = 1

29) AB = I
B = A^-1 . I
B = A^-1 = 1/-2 (1 ... -1) = (-1/2 ... 1/2)
......................... (-2 .. 0) .. (1 .......... 0)

30) (2 ... a) (x) = (5)
....... (b .. 6) (y) .. (7)

2x + ay = 5 => m1 = -x/y = -2/a
bx + 6y = 7 => m2 = -x/y = -b/6
Karena sejajar maka
m1 = m2
-2/a = -b/6
ab = 12