157×23/156
=(156+1)×23/156
=156*×23/156+23/156
=23又23/156
20.07×39+200.7×4.1+20×2×10.035
=20.07×39+20.07×41+20×20.07
=20.07×(39+41+20)
=20.07×100
=2007
99999^2+199999
=99999^2+199998+1
=99999^2+2×99999+1^2
=(99999+1)^2
=10^10