2 + 2 − 2 + 2 − … 2 2 2 2
If the value of the infinitely nested expression above equals x , find the value of 1 0 0 0 x .
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It is absolutely correct, however it can done without forming a fifth degree equation.
Try it by taking two variables.
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Yes I will add that too :D
Check my solution now
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I think there is a mistake. You have forgotten about negative sign while assuming y .
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@Akshay Yadav – I hope it is correct now :D
I don't follow the final steps in your first two solutions. Could you explain:
Solution 1) how you know that x^5 - x^4 - 4x^3 + 4x^2 is 0 for all x. For example, (-1)^5 - (-1)^4 - 4(-1)^3 + 4(-1)^2 = 6
Solution 2) I don't understand how the last two lines follow from the line above them
Let y = 2 − 2 + 2 − ⋯ 2 2 2 . Then we note that:
⎩ ⎪ ⎪ ⎨ ⎪ ⎪ ⎧ x = 2 + y 2 y = 2 − x 2 ⟹ x 2 = 2 + y 2 ⟹ y 2 = 2 − x 2 . . . ( 1 ) . . . ( 2 )
( 1 ) − ( 2 ) : x 2 − y 2 ( x − y ) ( x + y ) ⟹ x − y = y 2 + x 2 = x y 2 ( x + y ) = x y 2 . . . ( 3 )
( 1 ) + ( 2 ) : x 2 + y 2 x 2 + y 2 ⟹ x y = 4 + y 2 − x 2 = 4 + x y 2 ( x − y ) = 4 + ( x − y ) 2 = 4 + x 2 − 2 x y + y 2 = 2 ⟹ x = y 2 ( 3 ) : x y 2 = x − y
Therefore,
( 1 ) : x 2 ⟹ x 2 − x − 2 ( x − 2 ) ( x + 1 ) ⟹ x = 2 + y 2 = 2 + x = 0 = 0 = 2 ∵ x > 0
Then 1 0 0 0 x = 2 0 0 0 .
Nice solution sir!
First prove the convergence of a nested radical.
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x = 2 + 2 − 2 + … 2 2 2 S q u a r i n g B o t h S i d e s x 2 = 2 + 2 − 2 + … 2 2 2 ⟹ x 2 = 2 + 2 − x 2 2 ⟹ ( x 2 − 2 ) 2 = 2 − x 2 4 x 4 + 4 − 4 x 2 = 1 − x 1 2 ⟹ ( 1 − x 1 ) ( x 4 + 4 − 4 x 2 ) = 2 x 5 − x 4 − 4 x 3 + 4 x 2 + 2 x = 4 W e c a n s e e t h a t i f w e p u t a n y t h i n g i n t h e x i n x 5 − x 4 − 4 x 3 + 4 x 2 w e w i l l g e t 0 H e n c e w e c o u l d s e e t h a t o n l y t e r m l e f t i s 2 x T h e r e f o r e x = 2 a n d 2 ( x ) = 4
1 0 0 0 ∗ 2 = 2 0 0 0
A l t e r n a t i v e
W e m a y a l s o n o t i c e t h a t : x 5 − x 4 − 4 x 3 + 4 x 2 + 2 x = 4 x 5 − x 4 − 4 x 3 + 4 x 2 + 2 x − 4 = 0 x 5 − x 4 − x 3 − x 3 + x 2 + x − x 3 + x 2 + x − x 3 + x 2 + x 2 − 4 = 0 x 3 ( x 2 − x − 1 ) − x ( x 2 − x − 1 ) − x ( x 2 − x − 1 ) − x 3 + x 2 + x 2 − 4 = 0 ( x 3 − 2 x ) ( x 2 − x − 1 ) − x 3 + 2 x 2 − 4 = 0 ( x 3 − 2 x ) = x 3 − 2 x 2 + 4 ⟹ x 2 − x − 2 = 0 ⟹ ( x − 2 ) ( x + 1 ) = 0 ⟹ x = 2 ( O n l y )
A l t e r n a t i v e
L e t y b e s i m i l a r e q u a t i o n : y = 2 − x 2 a n d x = 2 + y 2 x 2 − y 2 = x 2 + y 2 ⟹ ( x + y ) ( x − y ) = x y x + y ⇒ x − y = x y 2 x + y ≆ 0 ( x − y ) x y = 2 ⇒ ( x − y ) = 2 x ( x − 2 ) = 2 And Complete further . . . .
x = 2