Geometriculus?

Geometry Level 5

Getting bored in my history class I started drawing some amazing triangles .

Starting from A A to B B then to C C and then again to A A (loop). Now extending C A CA to D D such that C A = A D CA=AD . Joining D B DB and extending B D BD to E E such that B D = B E BD=BE . Again joining C C and E E and extending C E CE to F F such that C E = C F CE=CF and so on indefinitely without lifting the pen (as shown in figure).

Denote the following symbols:

\bullet γ \gamma be the set containing lines parallel to A B AB .

\bullet β \beta be the set containing lines parallel to B C BC .

\bullet Δ \Delta be the set containing lines parallel to C D CD or C A CA .

\bullet Θ \Theta be the set containing lines parallel to D B DB or B E BE .

As i was getting extremely bored i drew 59 lines (assume)

We further denote the following:

a = n ( γ ) , b = n ( β ) , c = n ( Δ ) , d = n ( Θ ) a = n(\gamma), b = n(\beta), c = n(\Delta), d = n(\Theta)

Now the monic quartic equation whose roots are a , b , c , d a,b,c,d is "double derivated" (double differentiated) and it can be represented as g x 2 + e x + f = 0 g{ x }^{ 2 }+ex+f=0 .

Find the value of g + e + f + 24 |g| +|e|+|f| +24 .

Details and Assumptions

  • A B , B C , C D , D E AB, BC ,CD,DE are also included in the corresponding sets.

  • Consider C D , D E , E F , F G , G H CD,DE,EF,FG,GH and so on single line segments instead of two line segments.

This is original and the incident did happen.


The answer is 3000.

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1 solution

Caleb Townsend
Feb 3, 2015

First, define L n L_n as the n t h nth line drawn by the speaker, so that L 1 = A B , L 2 = B C , L 3 = C D , L 4 = D E , L_1 = \overline{AB}, L_2 = \overline{BC}, L_3 = \overline{CD}, L_4 = \overline{DE}, and so forth. Notice that L 1 L 5 , L 2 L 6 , L 3 L 7 , a n d L 4 L 8 . L_1 || L_5, \ L_2 || L_6, \ L_3 || L_7, \ and \ L_4 || L_8. More generally, L n L n + 4 , L_n || L_{n+4}, so the set of lines parallel to L n L_n will include all lines L m L_m where m n ( m o d 4 ) m \equiv n \pmod 4 and m 59 m \leq 59 since the speaker drew only 59 lines. This now gives
γ = { L 1 , L 5 , L 9 , . . . , L 57 } , n ( γ ) = 15 \gamma = \{L_1, L_5, L_9, ... , L_{57}\}, \ n(\gamma) = 15
β = { L 2 , L 6 , L 10 , . . . , L 58 } , n ( β ) = 15 \beta = \{L_2, L_6, L_{10}, ... , L_{58}\}, \ n(\beta) = 15
Δ = { L 3 , L 7 , L 11 , . . . , L 59 } , n ( Δ ) = 15 \Delta = \{L_3, L_7, L_{11}, ... , L_{59}\}, \ n(\Delta) = 15
Θ = { L 4 , L 8 , L 12 , . . . , L 56 } , n ( Θ ) = 14 \Theta = \{L_4, L_8, L_{12}, ... , L_{56}\}, \ n(\Theta) = 14


so the quartic polynomial with the above numbers as its roots will be of the form c ( x 15 ) 3 ( x 14 ) c(x-15)^3(x-14) where c c is a constant. For the purpose of this solution, let c = 1 c = 1 so that the needed polynomial is ( x 15 ) 3 ( x 14 ) = x 4 59 x 3 + 1305 x 2 12825 x + 47250. (x-15)^3(x-14) = x^4 - 59x^3 + 1305x^2 - 12825x + 47250. Differentiating this polynomial twice gives d 2 d x 2 ( x 15 ) 3 ( x 14 ) = 12 x 2 354 x + 2610. \frac{d^2}{dx^2} (x-15)^3(x-14) = 12x^2 - 354x + 2610.

Finally, the answer is obtained by adding 12 + 354 + 2610 + 24 = 3000 12 + 354 + 2610 + 24 = \boxed{3000}

Nice solution

Kudou Shinichi - 6 years, 4 months ago

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Hi, can you suggest some good books to refer for Algebra ?

Kudou Shinichi - 6 years, 4 months ago

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Here is one! ¨ \ddot\smile

Pranjal Jain - 6 years, 4 months ago

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@Pranjal Jain I also used to get bored in my history class :P

jaikirat sandhu - 6 years, 4 months ago

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@Jaikirat Sandhu Did you make any problem then?Just kidding

Gautam Sharma - 6 years, 3 months ago

Did the same way :)

Smarth Mittal - 6 years, 4 months ago

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