The Total solution for NCERT class 6-12
True.nth term of an A.P., an = a + (n – 1)da30 = a + (30 – 1 )d = a + 29dand a20 = a + (20 – 1 )d = a + 19d …(i)Now, a30 – a20 = (a + 29d) – (a + 19d) = 10dand from given A.P.common difference, d = -7 – (-3) = -7 + 3 = -4a30 – a20 = 10(-4) = -40 [from Eq- (i)]