f ( a , b ) = ( a + b ) 2 = ( a + b ) ( a + b ) = a 2 + a b + b a + b 2 = a 2 + 2 a b + b 2 {\displaystyle {\begin{alignedat}{3}f(a,b)&=(a+b)^{2}&&=(a+b)(a+b)\\&=a^{2}+ab+ba+b^{2}&&=a^{2}+2ab+b^{2}\\\end{alignedat}}}
