group x terms p(x)=(6x^2+24x)+21 factor out the quadratic coefient p(x)=6(x^2+4x)+21 take 1/2 of linear coefient and square it 4/2=2, 2^2=4 add negative and positive inside parenthasees p(x)=6(x^2+4x+4-4)+21 factor perfect square p(x)=6((x+2)^2-4)+21 expand p(x)=6(x+2)^2-24+21 p(x)=6(x+2)^2-3
