A=[–6e3tsin(3t) 6e2tcos(3t) –5e3tcos(3t) – 5e2tsin(3t)]
det A=–6e3tsin3t·(–5e2tsin3t–(–53t·cos3t·6e2t·cos3t)= =30e5t·(sin23t+cos23t)=30e5t·1=30e5t