jika ( 4 1 dibawahnya 3 a ) ( -1 a dibawahnya 2a - b 7 ) = ( 1 15 dibawahnya 7 20 ) maka nilai b adalah

[tex] \left[\begin{array}{ccc}4&1\\3&a\end{array}\right] [/tex] x [tex] \left[\begin{array}{cc}-1&a\\2a-b\end{array}\right] [/tex]=[tex] \left[\begin{array}{cc}1&15\\7&20\end{array}\right] [/tex]

[tex] \left[\begin{array}{cc}-4+2a-b&4a+7\\-3+2a^2-ab&3a+7a\end{array}\right] [/tex] = [tex] \left[\begin{array}{ccc}1&15\\7&20\end{array}\right] [/tex]

4a+7=15
4a=15-7
4a=8
a=8/4
a=2

-4+2a-b=1
-4+2.2-b=1
-4+4-b=1
-b=1
b=-1

Maka nilai b adalah -1