Which of the following are APs ? If they form an AP, find the common difference d and write three more terms.
– 1.2, – 3.2, – 5.2, – 7.2, . . .
–1.2, –3.2, –5.2, –7.2
a2 – a4 = –3.2 – (–1.2)
= –3.2 + 1.2
= –2.0
a3 – a2 = –5.2 – (–3.2)
= –5.2 + 3.2
= –2.0
a3 – a4
= –7.2 – (–5.2)
= –7.2 + 5.2
= –2.0
i.e., ak+1 – ak is the same every time. So, the given list of numbers forms an A .P. with the common difference d = – 2.0
The next three terms are :
– 7.2 + (–2.0) = –9.2
–9.2 + (–2.0) = –11.2
and –11.2 + (–2.0) = –13.2