bantu dong please :( nomor 3 4 dan 5 tolong yah :(

no.3
jawab: a = 2
          b = 2a ⇔2.2 = 4
          c = ab ⇔ 2.4 = 8
jadi a+b+c = 2+4+8 =14

no.4
jawab = [tex] \left[\begin{array}{ccc}3&1\\2&-2\end{array}\right] + 2 \left[\begin{array}{ccc}1&5\\-1&2\end{array}\right] [/tex]
          = [tex] \left[\begin{array}{ccc}3&1\\2&-2\end{array}\right] + \left[\begin{array}{ccc}2&10\\-2&4\end{array}\right] [/tex]
          = [tex] \left[\begin{array}{ccc}6-2&30+4\\4+4&20-8\end{array}\right] [/tex]
          = [tex] \left[\begin{array}{ccc}4&34\\8&16\end{array}\right] [/tex]
det [tex] \left[\begin{array}{ccc}4&34\\8&16\end{array}\right] [/tex] = 64-272 = -208
adjoint = [tex] \left[\begin{array}{ccc}4&34\\8&16\end{array}\right] [/tex]
           = [tex] \left[\begin{array}{ccc}16&-34\\-8&4\end{array}\right] [/tex]
[tex](A+2B) ^{-1} [/tex] = [tex] \left[\begin{array}{ccc}-1/13&17/104\\1/26&-1/52\end{array}\right] [/tex]

maaf kalo salah ya..

No 3.
[tex] \left[\begin{array}{ccc}5&a&3\\b&2&c\end{array}\right] = \left[\begin{array}{ccc}5&2&3\\2a&2&ab\end{array}\right][/tex]
cari yg seletak, maka:
*a = 2
*b=2a
 b=2x2=4
*c=a.b
 c=2x4=8
jadi a+b+c=2+4+8=14

4.
[tex] \left[\begin{array}{ccc}3&1\\2&-2\end{array}\right] + \left[\begin{array}{ccc}2&10\\-2&4\end{array}\right] = \left[\begin{array}{ccc}5&1\\0&2\end{array}\right] [/tex]
(A+2B)⁻¹ = 5x2 - 11x0
             = 10

5.
[tex] \left[\begin{array}{ccc}1&2\\4&3\end{array}\right] X \left[\begin{array}{ccc}3&1\\-2&-3\end{array}\right] = \left[\begin{array}{ccc}-1&-5\\-6&-5\\\end{array}\right] [/tex]

koreksi lagi ya :3

yg bonus
5x+y=-5      x2    10x+2y=-10 
2x+2y=14    x5    10x+10y=70
                           ------------------ -
                           -8y=-80
                             y=10

subsitusikan ke salah satu nya :
5x+y=-5
5x+10=-5
5x=-5-10
5x=-15
x=-3