is:
an = a1 + (n-1)d
Where:
n is the term number (n = 1, 2, 3, ...)
an is the nth term in the sequence
a1 is the first term in the sequence = -4
d is the common difference
To find the common difference, subtract any two successive terms: 1 - (-4) = 5, 6 - 1 = 5, 11 - 6 = 5. So we have d = 5. Hence the explicit form for this sequence is:
an = -4 + (n-1)5
To find a50, set n = 50 in the above formula and compute the answer.