Find the value of t7+t9 for the A.P. 9, 15, 21,27
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Correct Given:
- A.P : 9 , 15 , 22 , 29……
To find:
- t7 + t9
Solution:
A.P : 9 , 15 , 21 , 27……
Finding common difference
Common difference = t2 - t1
Where
- t1 = First term = a
- t2 = 2nd term
→ d = 15 - 9
→ d = 6
Using
tn = a + (n - 1)d
Where
- a : first term
- n : no. of terms
- d : common difference
→ t7 + t9 = a + (7 - 1)d + a + (9 - 1)d
→ t7 + t9 = 2(9) + 6(6) + 8(6)
→ t7 + t9 = 18 + 36 + 48
→ t7 + t9 = 102
Hence , t7 + t9 = 102
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