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December 20, 2014

December 20, 2014

Posted by **jen** on Friday, October 19, 2007 at 10:39pm.

Thanks so much xx

- maths -
**drwls**, Saturday, October 20, 2007 at 2:24amThe only solutions to 2r^2 - 3r -2 = 0 are

r = 2 and r = -1/2. You can prove that by factoring the equation.

The sequence a + ra + r^2 a + ...will not converge if r = 2. Therefore r must be -1/2.

Use the fact that the sum is 6 to figure out the first term, a

6 = a (1 -1/2 + 1/4 -1/8 + ...)

= a [1/(1 + (1/2))] = a*(2/3)

a = 9

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