The original worked lessons remain the main explanations. Use these focused reminders to check the conditions before you start.
Unknown constants and an integer exponent
Translate coefficient conditions into simultaneous equations.
Retain both signs and any zero cases before division.
Check that an inferred exponent is an admissible integer.
For \((1+ax)^n\), the first coefficients are \(na\) and \(\displaystyle \frac{n(n-1)}2a^2\). Check nonzero conditions before dividing. A finite binomial exponent in this package is a positive integer. An even power usually leaves two possible signs.