Question

Va rog nu ma descurc ​

Answer 1

Formula sumei primilor 9 termeni intr-o p.g este:

S9 = b1 x (q⁹ - 1)/(q - 1), intrucat q#1

S9 = 2 x [(1/2)⁹ - 1]/(1/2 - 1) amplifici pe primul 1 cu 512 si al doilea 1 cu 2

S9 = 2 x (1/512 - 512/512)/(1/2 - 2/2)

S9 = 2 x (-511/512)/(-1/2)

S9 = 511/512

Answer 2

$\it S_9=b_1\cdot\dfrac{1-q^9}{1-q}=2\cdot\dfrac{1-\dfrac{1}{2^9}}{1-\dfrac{1}{2}}=2\cdot\dfrac{\dfrac{2^9-1}{2^9}}{\dfrac{1}{2}}=2\cdot2\cdot\dfrac{512-1}{512}=\dfrac{511}{128}$