19 - 11.5 = 7.5
26.5 - 19 = 7.5
Difference = d = 7.5
Formula: an = a1 + d(n-1)
an = 7.5n + 4
See if the above formula is correct:
We know a1 = 19, let's prove it:
a1 = 7.5(1) + 4
a1 = 11.5
Now a2:
a2 = 7.5(2) + 4
a2 = 15 + 4
a2 = 19
Now that we know the above statement is correct, we can find 48th term:
a48 = 7.5(48) + 4
a48 = 364
//Hope it helps.
