The 21st term of an AP whose first two terms are - 3 and 4, is
first two terms of an AP are a = - 3 and a2 = 4.
As we know, nth term of an AP is
an = a + (n - 1)d
where a = first term
an is nth term
d is the common difference
a2 = a + d
4 = - 3 + d
d = 7
Common difference, d = 7
a21 = a + 20d
= - 3 + (20)(7)
= 137