+0  
 
0
1002
4
avatar+495 

Okay, this one is tough. I'm not sure it's even possible, but the experts on here are more knowledgeable than me, so let's get to it.

 

I need a function that goes through these points:

(1, 1)

(2, 1.6)

(3, 2.4)

(4, 3)

(5, 4)

(6, 5)

(7, 6.4)

(8, 8)

 

That's it! That's all I need. It might be super easy for a graphing expert but maybe not.

 

This is the best I've been able to come up with but it's not even close:

 

\(y = \frac{\left (\left ({x-1}\right )^{\frac{4}{3}} \right )}{2} +1\)

 

Any help would be SUPER appreciated!

 

EDIT: you can use any and as many exponents as you need and you can use any tricks to make it happen!

 Feb 26, 2016
edited by LambLamb  Feb 26, 2016

Best Answer 

 #2
avatar+26367 
+35

I need a function that goes through these points:

(1, 1)

(2, 1.6)

(3, 2.4)

(4, 3)

(5, 4)

(6, 5)

(7, 6.4)

(8, 8)

 

Function:  \(\begin{array}{rcll} y &=& ax^7 + bx^6 + cx^5 + dx^4 + ex^3 + fx^2 + gx + h \\ \end{array} \)

 

We have eight equations:

\(\begin{array}{rcll} 1 &=& a\cdot (1)^7 + b\cdot (1)^6 + c\cdot (1)^5 + d\cdot (1)^4 + e\cdot (1)^3 + f\cdot (1)^2 + g\cdot (1) + h \\ 1.6 &=& a\cdot (2)^7 + b\cdot (2)^6 + c\cdot (2)^5 + d\cdot (2)^4 + e\cdot (2)^3 + f\cdot (2)^2 + g\cdot (2) + h \\ 2.4 &=& a\cdot (3)^7 + b\cdot (3)^6 + c\cdot (3)^5 + d\cdot (3)^4 + e\cdot (3)^3 + f\cdot (3)^2 + g\cdot (3) + h \\ 3 &=& a\cdot (4)^7 + b\cdot (4)^6 + c\cdot (4)^5 + d\cdot (4)^4 + e\cdot (4)^3 + f\cdot (4)^2 + g\cdot (4) + h \\ 4 &=& a\cdot (5)^7 + b\cdot (5)^6 + c\cdot (5)^5 + d\cdot (5)^4 + e\cdot (5)^3 + f\cdot (5)^2 + g\cdot (5) + h \\ 5 &=& a\cdot (6)^7 + b\cdot (6)^6 + c\cdot (6)^5 + d\cdot (6)^4 + e\cdot (6)^3 + f\cdot (6)^2 + g\cdot (6) + h \\ 6.4 &=& a\cdot (7)^7 + b\cdot (7)^6 + c\cdot (7)^5 + d\cdot (7)^4 + e\cdot (7)^3 + f\cdot (7)^2 + g\cdot (7) + h \\ 8 &=& a\cdot (8)^7 + b\cdot (8)^6 + c\cdot (8)^5 + d\cdot (8)^4 + e\cdot (8)^3 + f\cdot (8)^2 + g\cdot (8) + h \\ \end{array}\)

 

We need the inverse Matrix of:

(  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,   {nl}    128.000000, 64.000000, 32.000000, 16.000000, 8.000000, 4.000000, 2.000000, 1.000000,   {nl}    2187.000000, 729.000000, 243.000000, 81.000000, 27.000000, 9.000000, 3.000000, 1.000000,   {nl}    16384.000000, 4096.000000, 1024.000000, 256.000000, 64.000000, 16.000000, 4.000000, 1.000000,   {nl}    78125.000000, 15625.000000, 3125.000000, 625.000000, 125.000000, 25.000000, 5.000000, 1.000000,   {nl}    279936.000000, 46656.000000, 7776.000000, 1296.000000, 216.000000, 36.000000, 6.000000, 1.000000,   {nl}    823543.000000, 117649.000000, 16807.000000, 2401.000000, 343.000000, 49.000000, 7.000000, 1.000000,   {nl}    2097152.000000, 262144.000000, 32768.000000, 4096.000000, 512.000000, 64.000000, 8.000000, 1.000000 )

 

The inverse Matrix is:

( -0.000198, 0.001389, -0.004167, 0.006944, -0.006944, 0.004167, -0.001389, 0.000198,

0.006944, -0.047222, 0.137500, -0.222222, 0.215278, -0.125000, 0.040278, -0.005556,

-0.101389, 0.663889, -1.862500, 2.902778, -2.715278, 1.525000, -0.476389, 0.063889,

0.798611, -4.972222, 13.312500, -19.888889, 17.923611, -9.750000, 2.965278, -0.388889,

-3.655556, 21.234722, -53.600000, 76.340278, -66.277778, 35.037500, -10.422222, 1.343056,

9.694444, -50.980556, 119.550000, -161.888889, 135.861111, -70.125000, 20.494444, -2.605556,

-13.742857, 62.100000, -133.533333, 172.750000, -141.000000, 71.433333, -20.600000, 2.592857,

8.000000, -28.000000, 56.000000, -70.000000, 56.000000, -28.000000, 8.000000, -1.000000 )

 

The coefficients (a,b,c,d,e,f,g,h) are:

a = -0.0013888889 {nl} b = 0.0441666667 {nl} c = -0.5747222222 {nl} d = 3.9375000000 {nl} e = -15.1805555556 {nl} f = 32.5183333333 {nl} g = -34.5433333333 {nl} h = 14.8000000000

 

The function is:

 

\(\small{ \begin{array}{rcll} y &=& -0.0013888889 \cdot x^7 + 0.0441666667\cdot x^6 -0.5747222222\cdot x^5 +\\ && +3.9375 \cdot x^4 -15.1805555556 \cdot x^3 + 32.5183333333\cdot x^2 -34.5433333333\cdot x + 14.8 \\ \end{array} }\)

 

or

\(\small{ \begin{array}{rcll} y &=& -\frac{1}{720} \cdot x^7 + \frac{53}{1200}\cdot x^6 -\frac{2069}{3600}\cdot x^5 + \frac{63}{16} \cdot x^4 -\frac{1093}{72} \cdot x^3 + 32.518\overline{3}\cdot x^2 -34.54\overline{3}\cdot x + \frac{74}{5} \\ \end{array} }\)

 

 

 

laugh

 Feb 26, 2016
edited by heureka  Feb 26, 2016
 #1
avatar+128460 
0

LambLamb....this is a VERY difficult thing to do  !!!!.......It can be managed with something called "LaGrange Polynomial Interpolation,' but this process is tedious even for a couple of points, much less eight of them....!!!!

 

I tried using WolframAlpha [ a very sophistacated online tool ].....it would handle up to the firstt five points, but after that, it apparently developed "sensory overload"  (LOL!!!!)

 

Perhaps some better mathematicians than me [ Alan, Bertie, Heureka, etc.] know how to do this using other techniques/resources......???

 

Sorry  !!!!!!

 

 

cool cool cool

 Feb 26, 2016
 #2
avatar+26367 
+35
Best Answer

I need a function that goes through these points:

(1, 1)

(2, 1.6)

(3, 2.4)

(4, 3)

(5, 4)

(6, 5)

(7, 6.4)

(8, 8)

 

Function:  \(\begin{array}{rcll} y &=& ax^7 + bx^6 + cx^5 + dx^4 + ex^3 + fx^2 + gx + h \\ \end{array} \)

 

We have eight equations:

\(\begin{array}{rcll} 1 &=& a\cdot (1)^7 + b\cdot (1)^6 + c\cdot (1)^5 + d\cdot (1)^4 + e\cdot (1)^3 + f\cdot (1)^2 + g\cdot (1) + h \\ 1.6 &=& a\cdot (2)^7 + b\cdot (2)^6 + c\cdot (2)^5 + d\cdot (2)^4 + e\cdot (2)^3 + f\cdot (2)^2 + g\cdot (2) + h \\ 2.4 &=& a\cdot (3)^7 + b\cdot (3)^6 + c\cdot (3)^5 + d\cdot (3)^4 + e\cdot (3)^3 + f\cdot (3)^2 + g\cdot (3) + h \\ 3 &=& a\cdot (4)^7 + b\cdot (4)^6 + c\cdot (4)^5 + d\cdot (4)^4 + e\cdot (4)^3 + f\cdot (4)^2 + g\cdot (4) + h \\ 4 &=& a\cdot (5)^7 + b\cdot (5)^6 + c\cdot (5)^5 + d\cdot (5)^4 + e\cdot (5)^3 + f\cdot (5)^2 + g\cdot (5) + h \\ 5 &=& a\cdot (6)^7 + b\cdot (6)^6 + c\cdot (6)^5 + d\cdot (6)^4 + e\cdot (6)^3 + f\cdot (6)^2 + g\cdot (6) + h \\ 6.4 &=& a\cdot (7)^7 + b\cdot (7)^6 + c\cdot (7)^5 + d\cdot (7)^4 + e\cdot (7)^3 + f\cdot (7)^2 + g\cdot (7) + h \\ 8 &=& a\cdot (8)^7 + b\cdot (8)^6 + c\cdot (8)^5 + d\cdot (8)^4 + e\cdot (8)^3 + f\cdot (8)^2 + g\cdot (8) + h \\ \end{array}\)

 

We need the inverse Matrix of:

(  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,   {nl}    128.000000, 64.000000, 32.000000, 16.000000, 8.000000, 4.000000, 2.000000, 1.000000,   {nl}    2187.000000, 729.000000, 243.000000, 81.000000, 27.000000, 9.000000, 3.000000, 1.000000,   {nl}    16384.000000, 4096.000000, 1024.000000, 256.000000, 64.000000, 16.000000, 4.000000, 1.000000,   {nl}    78125.000000, 15625.000000, 3125.000000, 625.000000, 125.000000, 25.000000, 5.000000, 1.000000,   {nl}    279936.000000, 46656.000000, 7776.000000, 1296.000000, 216.000000, 36.000000, 6.000000, 1.000000,   {nl}    823543.000000, 117649.000000, 16807.000000, 2401.000000, 343.000000, 49.000000, 7.000000, 1.000000,   {nl}    2097152.000000, 262144.000000, 32768.000000, 4096.000000, 512.000000, 64.000000, 8.000000, 1.000000 )

 

The inverse Matrix is:

( -0.000198, 0.001389, -0.004167, 0.006944, -0.006944, 0.004167, -0.001389, 0.000198,

0.006944, -0.047222, 0.137500, -0.222222, 0.215278, -0.125000, 0.040278, -0.005556,

-0.101389, 0.663889, -1.862500, 2.902778, -2.715278, 1.525000, -0.476389, 0.063889,

0.798611, -4.972222, 13.312500, -19.888889, 17.923611, -9.750000, 2.965278, -0.388889,

-3.655556, 21.234722, -53.600000, 76.340278, -66.277778, 35.037500, -10.422222, 1.343056,

9.694444, -50.980556, 119.550000, -161.888889, 135.861111, -70.125000, 20.494444, -2.605556,

-13.742857, 62.100000, -133.533333, 172.750000, -141.000000, 71.433333, -20.600000, 2.592857,

8.000000, -28.000000, 56.000000, -70.000000, 56.000000, -28.000000, 8.000000, -1.000000 )

 

The coefficients (a,b,c,d,e,f,g,h) are:

a = -0.0013888889 {nl} b = 0.0441666667 {nl} c = -0.5747222222 {nl} d = 3.9375000000 {nl} e = -15.1805555556 {nl} f = 32.5183333333 {nl} g = -34.5433333333 {nl} h = 14.8000000000

 

The function is:

 

\(\small{ \begin{array}{rcll} y &=& -0.0013888889 \cdot x^7 + 0.0441666667\cdot x^6 -0.5747222222\cdot x^5 +\\ && +3.9375 \cdot x^4 -15.1805555556 \cdot x^3 + 32.5183333333\cdot x^2 -34.5433333333\cdot x + 14.8 \\ \end{array} }\)

 

or

\(\small{ \begin{array}{rcll} y &=& -\frac{1}{720} \cdot x^7 + \frac{53}{1200}\cdot x^6 -\frac{2069}{3600}\cdot x^5 + \frac{63}{16} \cdot x^4 -\frac{1093}{72} \cdot x^3 + 32.518\overline{3}\cdot x^2 -34.54\overline{3}\cdot x + \frac{74}{5} \\ \end{array} }\)

 

 

 

laugh

heureka Feb 26, 2016
edited by heureka  Feb 26, 2016
 #3
avatar
0

@ CPhill - Thanks so much for trying!

 

@ Heureka - Thanks so much for the time and effort‼

 

-LambLamb

 Feb 26, 2016
edited by Guest  Feb 26, 2016
 #4
avatar+128460 
+5

Thanks, heureka......that was impressive!!!!

 

See, LambLamb??.....I thought someone on here might be able to do this!!!!....

 

 

 

cool cool cool

 Feb 26, 2016

3 Online Users

avatar
avatar