x^2-6x+15=x^2-2*x*3+3^2-3^2+15=(x-3)^2-9+15=(x-3)^2+6
x^2+x+1=x^2+2*x*0.5+0.5^2-0.5^2+1=(x+0.5)^2-0.25+1=(x+0.5)^2+0.75
x^2-6x+15=x^2-2*x*3+3^2-3^2+15=(x-3)^2-9+15=(x-3)^2+6
x^2+x+1=x^2+2*x*0.5+0.5^2-0.5^2+1=(x+0.5)^2-0.25+1=(x+0.5)^2+0.75