(8a³b-5a²b²)/4ab
=8a³b÷4ab-5a²b²÷4ab
=8÷4×(a³÷a)×(b÷b)-5÷4×(a²÷a)×(b²÷b)
=2×a²×1-(5/4)×a×b
=2a²-(5/4)ab