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F5 Maths
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最佳解答:
Given a=5, a+ar+ar^2=31/5 a(1+r+r^2)=31/5 5(1+r+r^2)=31/5 1+r+r^2=31/25 25r^2+25r+25=31 25r^2+25r-6=0 (5r-1)(5r+6)=0 r=1/5 or -6/5 The common ratios are1/5 or -6/5.
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F5 Maths
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If the first term of a geometric sequence is 5 and the sum of the first three terms is 31/5, find the common ratio(s).最佳解答:
Given a=5, a+ar+ar^2=31/5 a(1+r+r^2)=31/5 5(1+r+r^2)=31/5 1+r+r^2=31/25 25r^2+25r+25=31 25r^2+25r-6=0 (5r-1)(5r+6)=0 r=1/5 or -6/5 The common ratios are1/5 or -6/5.
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