Paralyzing Progressions!

Algebra Level 2

Find the sum of the values of x x and y y if ( x + y ) (x+y) , ( 2 x + 1 ) (2x+1) , ( 3 x 1 ) (3x-1) are in A P AP and x x , x y xy and ( 3 x + 10 y ) (3x+10y) are in G P GP .


The answer is 8.

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2 solutions

Shimul Dey
Apr 3, 2014

F r o m A P w e c a n w r i t e , ( 2 x + 1 ) ( x + y ) = ( 3 x 1 ) ( 2 x + 1 ) = > x y + 1 = x 2 = > y = 1 + 2 S o , y = 3 F r o m G P w e c a n w r i t e , x y x = 3 x + 10 y x y = > y = 3 x + 10 y x y = > 3 = 3 x + 30 3 x [ s i n c e , y = 3 ] = > 3 x = x + 10 = > 2 x = 10 S o , x = 5 N o w S u m o f x & y i s , x + y = 3 + 5 = 8 From\quad AP\quad we\quad can\quad write,\\ (2x+1)\quad -\quad (x+y)\quad =\quad (3x-1)-(2x+1)\\ =>\quad x-y+1\quad =\quad x-2\\ =>\quad y\quad =\quad 1+2\\ So,\quad y\quad =\quad 3\\ \\ From\quad GP\quad we\quad can\quad write,\\ \frac { xy }{ x } \quad =\quad \frac { 3x+10y }{ xy } \\ =>\quad y\quad =\quad \frac { 3x+10y }{ xy } \\ =>\quad 3\quad =\quad \frac { 3x\quad +\quad 30 }{ 3x } \quad [since,\quad y=3]\\ =>\quad 3x\quad =\quad x\quad +\quad 10\\ =>\quad 2x\quad =\quad 10\\ So,\quad x\quad =\quad 5\\ \\ Now\quad Sum\quad of\quad x\quad \& \quad y\quad is,\\ x\quad +\quad y\quad =\quad 3\quad +\quad 5\quad =\quad 8 .

Hello all,

as for arithmetic progression(AP), use common difference,

(2x+1) - (x+y) = (3x-1) - (2x+1)

x + 1 -y = x -1 -1

1-y = -2

y =1 + 2 = 3

as for geometric progression(GP),use common ratio,

xy / x = (3x+10y) / xy (1)

substitute y=3 into this (1),

3x / x = (3x + 30) / 3x

(3x)(3x) = x(3x + 30)

9x^2 = 3x^2 + 30x

6x^2 - 30x = 0

6x(x - 5) = 0

x=0, or x=5,

Therefore sum of values of x and y are = 0 + 5 + 3 =8,

Thanks...

Exactly how I worked it out.

Oliver Daniel - 7 years, 2 months ago

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