f ( a , b ) = ( a + b ) 5 = ( a + b ) ( a + b ) = a 5 + a b + b a + b 5 = a 5 + 5 a b + b 5 {\displaystyle {\begin{alignedat}{3}f(a,b)&=(a+b)^{5}&&=(a+b)(a+b)\\&=a^{5}+ab+ba+b^{5}&&=a^{5}+5ab+b^{5}\\\end{alignedat}}}
