Номер 399,401,помогииитк

399)  [latex]4a^2b^2+4ab+1= (2ab)^2+2*2ab+1=(2ab+1)^2 [/latex] [latex]1-xy+ \frac{x^2y^2}{4}=1-2* \frac{1}{2}xy+( \frac{xy}{2})^2=(1- \frac{xy}{2})^2 [/latex] 401) [latex]12a^3x-36a^2bx+27ab^2x=3ax(4a^2-12ab+9b^2)=3ax(2a+3b)^2[/latex] [latex]2a^2b^3-28ab^2+98b=2b(a^2b^2-14ab+49)=2b(ab-7)^2[/latex]