This Binomial Theorem Video explains how to find the term independent of x is a clear and concise manner. His method of finding the r value is exactly the same way i use to teach my students, this method reduces the chance of students making mistakes.

Additional Math (Amath) Small Group Math Tuition. Woodlands, Yew Tee, Choa Chu Kang, Sembawang, Yishun and Johor Bahru (JB) Malaysia