(100-10x-x)(100+10x)=216010000-1100x+1000x-110x²-2160=0110x²+100x-7840=011x²+10x-784=0x=-10±√(10²+4*11*784)/2*11 =-10±√34496/22 =-10±√1568 =-10±28√2∴x=-10±28√2