ABSTRACT
Solution The coefficient of x7 is 4 because when the terms in the first bracket are multiplied by those in the second bracket we obtain just four terms of degree seven, namely, x ⋅ x6, x3 ⋅ x4, x5 ⋅ x2, and x7 ⋅ 1, or, as we now prefer to write them,
x ⋅ x6, x3 ⋅ x4, x5 ⋅ x2, x7 ⋅ x0.
