Bài 2:
a: \(10x+86=16+5x\)
=>10x-5x=16-86
=>5x=-70
=>\(x=-\frac{70}{5}=-14\)
b: \(14x-11=-43+18x\)
=>\(14x-18x=-43+11\)
=>-4x=-32
=>x=8
c: \(72-3x=-\left(5x+8\right)\)
=>\(72-3x+5x+8=0\)
=>2x+80=0
=>2x=-80
=>x=-40
d: \(-\left(15x-31\right)=-12x+4\)
=>15x-31=12x-4
=>15x-12x=-4+31
=>3x=27
=>x=9
e: \(25-\left(x+30\right)=x-\left(27-8\right)\)
=>25-x-30=x-19
=>-x-5=x-19
=>-x-x=-19+5
=>-2x=-14
=>x=7
f: (x-12)-15=(20-7)-(x+18)
=>x-27=13-x-18=-5-x
=>x+x=-5+27
=>2x=22
=>x=11
Bài 3:
a: \(a-b+\left(a+b-c\right)-\left(a-b-c\right)\)
=a-b+a+b-c-a+b+c
=a+b
b: a-(b-c+d)+(c-d-a+b)
=a-b+c-d+c-d-a+b
=2c-2d=2(c-d)
c: (a+b)(c-d)-a(c-d)
=(c-d)(a+b-a)
=b(c-d)
d: (a-b)(c-d)-b(d-c)
=(a-b)(c-d)+b(c-d)
=(c-d)(a-b+b)
=a(c-d)
