2x方-3x+2x根号x方-3x+4=21
2x^2-3x+2x√(x^2-3x+4)=21
x^2-3x+4+2x√(x^2-3x+4)+x^2=25
[√(x^2-3x+4)+x]^2=25
√(x^2-3x+4)+x=±5
√(x^2-3x+4)+x=5
√(x^2-3x+4)=5-x
x^2-3x+4=25+x^2-10x
7x=21
x=3
或
√(x^2-3x+4)+x=-5
√(x^2-3x+4)=-5-x
x^2-3x+4=25+x^2+10x
13x=-21
x=-21/13