The function is symmetric about x=2 and x=7, so all necessary zero are found by reflecting x=0 repeatedly about x=2 and x=7; if is a reflection about x=2 and about x=7, then we obtain a sequence of zeros or . If is our first reflection, then we obtain the following sequence of zeros and in general , giving us 200+202 = 402 zeros in the interval [-2007, 2007]. If is our first reflection, then we get the sequence , which yields another 402 zeros. A quick check shows that the two sequences have no terms in common. Hence at least 804 zeros total in [-2007, 2007].