ba²-5a(－a+b+1)+4a(3a+2)
=ba²＋5a²－5ab-5a+12a²＋8a
＝ba²＋17a²－5ab＋3a
代入a=2,b=1/20
=4／20＋20－1／2＋6
=25.7