Bài 1
5{[ 85-[6² -1] ÷ 7]÷ 8 +10.3²}-10²
=5{[ 85-[36 -1] ÷ 7]÷ 8 +10.9}-100
=5{[ 85-35 ÷ 7]÷ 8 +90}-100
=5{[ 85-5]÷ 8 +90}-100
=5{80÷ 8 +90}-100
=5{10 +90}-100
=5.100-100
=500-100=400
bài 2:
[4²-1].[x-1].2=6
[16-1].[x-1]=6:2
15.[x-1]=3
x-1=3:15
x-1=0,2
x=0,2+1
x=1,2