To find the 50th term in this sequence, first you need to find how what the sequence is. To get from 5 to -2 you're subtracting 7, to get from -2 to -9, you subtract another 7. In order to get the next number you go down by multiples of 7: 5 - 7 = -2; 5 - 14 = -9 and so on). So all you have to do is multiply 7 by 50 to get 350 and subtract that from 5 to get -345.
Hope this helps,
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