Question 12***+Use the binomial theorem to explain why the coefficients of \((x+y)^4\) are \(1,4,6,4,1\).
Question 17****+In \((a+b)^n\), determine which term contains \(a^3b^{n-3}\), and state its coefficient.
Question 20*****Find the coefficient of \(x^0\) in \((3x^2-\frac{1}{x})^{12}\), or explain why no such term exists.