Let x1(0) = initial condition for X1
x2(0) = initial condition for X2
The equations from the matrix are
X1' = 4X1 - 3X2
X2' = 3X1 + 4X2
When you solve the equations simultaneously, you obtain the following for X1 & X2
X1 = (e4xcos3x)x1(0) - (e4xsin3x)x2(0)
X2 = (e4xsin3x)x1(0) + (e4xcos3x)x2(0)