1.

If 4th term of any G.P. is p, 7th term is q and 10th term is r, then prove that q2 – pr.

Answer»

Let a is first term and R is common ratio of G.P., then according to question

T4 = aR4 – 1

p = aR3           ….. (i)

T7 = aR7 – 1

q = aR6           ….. (ii)

T10 = aR10 – 1

r = aR9            ….. (iii)

Multiplying equation (i) and (iii), we get

aR12 = pr    ….. (iv)

Squaring of equation (ii),

q2 = aR12 Hence, from equation (iv) and (v)

q2 = pr         ….. (v)

Hence Proved.



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