Ditentukan : [tex] 2 \left[\begin{array}{cc}-a&b+2\\c-4&d\end{array}\right] + \left[\begin{array}{cc}4&b+c\\8&2d\end{array}\right] = \left[\begin{array}{cc}10&-

2(-a) + 4=10
-2a = 10 - 4
-2a = 6
a = -3

2(c-4) + 8 = -4
2c - 8 + 8 = -4
2c = -4
c = -2

2(b+2) + (b+c) = -7
2b + 4 + b + c = -7
3b + c = -7 - 4
3b + c = -11
3b -2 = -11
3b = -11 + 2
3b = -9
b = -3

2d  +2d = a-1
4d = -3-1
4d = -4
d = -1

a+b+c+d = (-3) + (-3) + (-2) + (-1) = -3-3-2-1 = -9

semoga membantu ya.. :)