Lg(12-x)(8+x)= lg 100
(12-x)(8+x)=100
96+12x-8x-x²=100
96+4x-x²=100
x²-4x-96+100=0
x²-4x+4=0
(x-2)²=0
x=2
Lg(12-x)(8+x)= lg 100
(12-x)(8+x)=100
96+12x-8x-x²=100
96+4x-x²=100
x²-4x-96+100=0
x²-4x+4=0
(x-2)²=0
x=2