a 12 a^{12} + b 12 b^{12} + c 12 c^{12} + d 12 d^{12} + e 12 e^{12} wanted

Algebra Level 5


The answer is 45797.

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2 solutions

Chew-Seong Cheong
Oct 11, 2015

Let P n = a n + b n + c n + d n + e n P_n = a^n + b^n + c^n + d^n + e^n , where n n is a positive integer, and

S 1 = c y c 5 a = P 1 = 1 S 2 = c y c 5 a b S 3 = c y c 5 a b c S 4 = c y c 5 a b c d S 5 = a b c d e S_1 = \displaystyle \sum_{cyc}^5 a = P_1 = 1 \quad \quad S_2 = \sum_{cyc}^5 ab \quad \quad S_3 = \sum_{cyc}^5 abc \quad \quad S_4 = \sum_{cyc}^5 abcd \quad \quad S_5 = abcde

Using Newton sums method, we have:

\(\begin{array} {} P_1 = S_1 = 1 & \Rightarrow S_1 = 0 \\ P_2 = S_1P_1 - 2S_2 = 1 & \Rightarrow S_2 = 0 \\ P_3 = S_1P_2 - S_2P_1 + 3S_3 = 2 & \Rightarrow S_3 = \frac{1}{3} \\ P_4 = S_1P_3 - S_2P_2 + S_3P_1 - 4S_4 = 3 & \Rightarrow S_4 = - \frac{1}{6} \\ P_5 = S_1P_4 - S_2P_3 + S_3P_2 - S_4P_1 + 5S_5 = 5 & \Rightarrow S_5 = \frac{3}{10} \end{array} \)

For n > 5 n > 5 , we have P n = S 1 P n 1 S 2 P n 2 + S 3 P n 3 S 4 P n 4 + S 5 P n 5 P_n = S_1P_{n-1} - S_2P_{n-2} + S_3P_{n-3} - S_4P_{n-4} + S_5P_{n-5} .

Using the following Excel spreadsheet we found that P 12 = a 12 + b 12 + c 12 + d 12 + e 12 = 47147 1350 P_{12} = a^{12} + b^{12} + c^{12} + d^{12} + e^{12} = \dfrac{47147}{1350} .

Therefore, m n = 45797 m-n = \boxed{45797}

I have actually learnt from you. Thanks for these!

Lu Chee Ket - 5 years, 8 months ago

Two columns of cross multiplications and additions with $ shall achieve for all n to quite a huge number using Excel.

Lu Chee Ket - 5 years, 8 months ago

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You should try this one . You should learn up LaTex. Just put your mouse-cursor on top of the formulas and you can see the entered codes.

Chew-Seong Cheong - 5 years, 8 months ago

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I have just tried the one. All right and I have tried a bit with LaTex and I have seen the codes.

Lu Chee Ket - 5 years, 8 months ago

I used Newton sum till i got the answer...

Dev Sharma - 5 years, 7 months ago

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I was also using Newton sums. It was just that I used a spreadsheet to do the computation.

Chew-Seong Cheong - 5 years, 7 months ago
Lu Chee Ket
Oct 11, 2015

S1 = 1; 1: P1 = 1

S2 = 0; 1: P2 = 1

S3 = 1/3; 2: P3 = 2

S4 = -1/6; 3: P4 = 3

S5 = 0.3; 5: P5 = 5

S6 = 0; 8: P6 = 6.13333333333333 92 15 77

S7 = 0; 13: P7 = 7.76666666666667 233 30 203

S8 = 0; 21: P8 = 10.5333333333333 158 15 143

S9 = 0; 34: P9 = 14.3111111111111 644 45 599

S10 = 0; 55: P10 = 19.4222222222222 874 45 829

S11 = 0; 89: P11 = 26.0677777777778 23461 900 22561

S12 = 0; 144: P12 = 34.9237037037037 47147 1350 45797

363127

The non-mentioned things behind these are actually Complex Numbers which allow all these to happen in validity; once a, b, c, d and e are fixed, all are just fixed:

a = 1.344665235633880

b = 0.276584727888310 + j 0.699496514084196

c = 0.276584727888310 - j 0.699496514084196

d = -0.448917345705252 + j 0.439081791607579

e = -0.448917345705252 - j 0.439081791607579

However, they are not the preference for evaluation of a^n + b^n + c^n + d^n + e^n but Newton sums method is the way; evaluation using Excel can be most accurate for n of high power. Nevertheless, COMPLEX and IMPOWER and etc allow us to do arithmetic of complex numbers in Microsoft Excel.

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