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  • Find the sum to indicated number of terms in each of the geometric progressions in square root 7 square root 21 3 square root 7 n terms

 8.  Find the sum to indicated number of terms in each of the geometric progressions in  

         \sqrt 7 , \sqrt {21} , 3 \sqrt 7 ,.... n \: \: terms

Answers (1)

best_answer

GP=\sqrt 7 , \sqrt {21} , 3 \sqrt 7 ,...............

a=\sqrt{7}\, \, \, \, and\, \, \, \, \, r=\frac{\sqrt{21}}{\sqrt{7}}=\sqrt{3}

S_n=\frac{a(1-r^n)}{1-r}

S_n=\frac{\sqrt{7}(1-\sqrt{3}^n)}{1-\sqrt{3}}

S_n=\frac{\sqrt{7}(1-\sqrt{3}^n)}{1-\sqrt{3}}\times \frac{1+\sqrt{3}}{1+\sqrt{3}}

S_n=\frac{\sqrt{7}(1-\sqrt{3}^n)}{1-3} (1+\sqrt{3})

S_n=\frac{\sqrt{7}(1-\sqrt{3}^n)}{-2} (1+\sqrt{3})

S_n=\frac{\sqrt{7}(1+\sqrt{3})}{2} (\sqrt{3}^n-1)

Posted by

seema garhwal

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