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.

SeQuEnCeS and SeRiEs: HELP PLZ!  Steve, Friday, January 4, 2013 at 2:28pm
yx = x+8
y/x = 72/y
y = 2x+8
(2x+8)/x = 72/(2x+8)
4x^2+32x+64 = 72x
4x^240x+64 = 0
x^2  10x + 16 = 0
(x2)(x8) = 0
x=2,8
y=12,24
so, we have
8,2,12,72
or
8,8,24,72

SeQuEnCeS and SeRiEs: HELP PLZ!  kazz, Friday, January 4, 2013 at 2:33pm
thanks:)
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