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a G.P has 6 terms .if the 3rd term and the 4th terms are 28 and -56 respectively.find the common ratio,the first term ,and the sum of the G.P​

User Jeff Pratt
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16 votes
16 votes

Answer:

Hello,

Explanation:


u_2=u_1*r\\u_3=u_1*r^2\\u_4=u_1*r^3\\\\(u_4)/(u_3) =r=(-56)/(28) =\boxed{-2}\\\\u_1=(u_3)/(r^2) =(28)/((-2)^2) =(28)/(4)=\boxed {7}\\\\\\\displaystyle\ s=\sum_(i=1)^6\ u_i\\\\=u_1*\sum_(i=1)^6\ r^(i-1)\\\\=7*((-2)^6-1)/(-2-1) \\\\=-7*(65)/(3) \\\\\\\boxed{s=-(455)/(3) }\\

User Jevgenij Dmitrijev
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