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NCERT Class XI Mathematics - Sequences and Series - Solutions

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Question : 37 of 106
Marks: +1, -0
The 4th term of a G.P. is square of its second term, and the first term is – 3. Determine its 7th term.
Solution:  
We have a = – 3, a4a_4 = (a2)2(a^2)^2
⇒ ar3ar^3 = (ar)2(ar)^2 ⇒ ar3ar^3 = a2r2a^2r^2 ⇒ r = a = – 3 (Since a = – 3)
∴ a7a_7 = ar6ar^6 = – 3 (–3)6(– 3)^6 = –2187
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