Materi matriks kelas 11. Bantu nomor 5,6,7,8. Pake langkah penyelesaian. Makasih

jawab
5)
[tex] \left[\begin{array}{ccc}a&b\end{array}\right] \left[\begin{array}{ccc}a\\b\end{array}\right] = \left[\begin{array}{ccc}61\end{array}\right] [/tex]

a² + b² = 61
b = a+ 1
a² + (a + 1)² = 61
a² + a² + 2a + 1 = 61
2a² + 2a -60 = 0
a² + a - 30 = 0
(a +6)(a-5)=0
a = -6 atau a= 5 , dan a ,b  bulat positip , maka a = 5 
a + b = a + a + 1 = 2a + 1 = 2(5)+ 1= 11

6)
[tex]3 \left[\begin{array}{ccc}3&-1\\1&0\end{array}\right]\,-D\,=\,\left[\begin{array}{ccc}5&-9\\7&-2\end{array}\right][/tex]

[tex]D\,=\,3 \left[\begin{array}{ccc}3&-1\\1&0\end{array}\right]\,- \left[\begin{array}{ccc}5&-9\\7&-2\end{array}\right][/tex]

[tex]D\,=\, \left[\begin{array}{ccc}9&-3\\3&0\end{array}\right]\,- \left[\begin{array}{ccc}5&-9\\7&-2\end{array}\right]\,=\, \left[\begin{array}{ccc}4&6\\-4&2\end{array}\right][/tex]

7)
[tex] \left[\begin{array}{ccc}x\\y\end{array}\right]\,=\, \left[\begin{array}{ccc}2&1\\0&2\end{array}\right] \, \left[\begin{array}{ccc}3\\2\end{array}\right]\,+\, \left[\begin{array}{ccc}4\\1\end{array}\right][/tex]

[tex]\left[\begin{array}{ccc}x\\y\end{array}\right]\,=\, \left[\begin{array}{ccc}8\\4\end{array}\right] \,+\, \left[\begin{array}{ccc}4\\1\end{array}\right]\,= \left[\begin{array}{ccc}12\\5\end{array}\right][/tex]

x - y = 12 - 5 = 7

8)
[tex] \left[\begin{array}{ccc}2&1\\a+b&5\end{array}\right]\,+\, \left[\begin{array}{ccc}3&b\\1-&5\end{array}\right]\,=\, \left[\begin{array}{ccc}5&-3\\9&10\end{array}\right][/tex]

[tex]\left[\begin{array}{ccc}5&1+b\\a+b+10&10\end{array}\right]\,=\, \left[\begin{array}{ccc}5&-3\\9&10\end{array}\right][/tex]

1 + b = - 3 
b = - 4

a +b+ 10 = 9
a +b = - 1
a = - 1 - b
a = - 1 - (-4)
a = 3