Chapter 8
Predicting What Comes Next: Exploring Sequences and Progressions
CBSE Class 9
Mathematics Solutions
Educart Mathematics class Class 9 NCERT Exemplar cover
Question:

Determine the AP whose third term is 16 and whose 7th7^{\text{th}} term exceeds the 5th5^{\text{th}} term by 12.

Answer: Verified

Let a=a = first term, d=d = common difference

Third term: a3=a+2d=16a_3 = a + 2d = 16 ...(i)

Also, a7a5=12a_7 - a_5 = 12

(a+6d)(a+4d)=12(a + 6d) - (a + 4d) = 12

2d=122d = 12

d=6d = 6

Put d=6d = 6 in (i):

a+2(6)=16a+12=16a=4\begin{aligned} a + 2(6) &= 16 \\ a + 12 &= 16 \\ a &= 4 \end{aligned}

Therefore, the AP is 4, 10, 16, 22, 28, ...

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