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posted by kazz on Friday, January 4, 2013 at 2:19pm.

The first three terms of the sequence -8,x,y,72... form an arithmetic sequence, while the second, third and fourth terms form a geometric sequence. Determine x and y.

y-x = x+8 y/x = 72/y y = 2x+8 (2x+8)/x = 72/(2x+8) 4x^2+32x+64 = 72x 4x^2-40x+64 = 0 x^2 - 10x + 16 = 0 (x-2)(x-8) = 0 x=2,8 y=12,24 so, we have -8,2,12,72 or -8,8,24,72

thanks:-)

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