MCQ
In an A.P. first two terms are – 3, 4 then 21st term is . . .
- A
- B
- ✓
- D
✓
Answer
Correct option: C.
(C) 137
Given: first term a = – 3
Second term t1 = 4
Common difference d = t1 – a = 4 – ( – 3) = 4 + 3 = 7
We need to find t21 where n = 21
Now, By using nth term of an A.P. formula
tn = a + (n – 1)d
where n = no. of terms
a = first term
d = common difference
tn = nth terms
Substituting all given value in the formulae we get,
⇒ t21 = – 3 + (21 – 1) × 7
⇒ t21 = – 3 + 20 × 7
⇒ t21 = – 3 + 140 = 137
Hence, correct answer is (C)
Given: first term a = – 3
Second term t1 = 4
Common difference d = t1 – a = 4 – ( – 3) = 4 + 3 = 7
We need to find t21 where n = 21
Now, By using nth term of an A.P. formula
tn = a + (n – 1)d
where n = no. of terms
a = first term
d = common difference
tn = nth terms
Substituting all given value in the formulae we get,
⇒ t21 = – 3 + (21 – 1) × 7
⇒ t21 = – 3 + 20 × 7
⇒ t21 = – 3 + 140 = 137
Hence, correct answer is (C)
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