Let f(x)=∑n=0∞anxn. Which statement correctly describes the coefficient of xn in the series for x3f(x)?
a) It equals an−3 for n≥3 and 0 for n<3. (correct)
b) It equals an+3 for all n≥0.
c) It equals 3an for all n≥0.
d) It equals 0 for n<3 and 3an−3 for n≥3.