If H = {(1,-4), (2,-3), (3,-2), (4,-1),...), What is H(9)?

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If H = {(1,-4), (2,-3), (3,-2), (4,-1),...), What is H(9)?

It looks like each x-coordinate goes up by 1 and each y-coordinate decreases by 1. Their difference is 5. So we have:
H(9) = (9, 4)