finding values of a b c d

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xoxox
xoxox on 6 Feb 2018
Edited: Stephen23 on 6 Feb 2018
Hi, Can anyone help me with this. I have no idea how to find the value of a b c d. PLEASE LOOK AT THE PICTURE! THANKS!
  1 Comment
Stephen23
Stephen23 on 6 Feb 2018
Edited: Stephen23 on 6 Feb 2018
It is not required to use slow and complex symbolic operations. See Andrei Bobrov's answer for the fast, efficient, and simple numeric solution.

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Accepted Answer

Birdman
Birdman on 6 Feb 2018
syms a b c d
eq=[5;-17;14;9]==[2 2 -7 2;3 2 -5 6;9 -8 1 -4;1 5 3 -1]*[a;b;c;d]
sol=solve(eq)
a=vpa(sol.a,4)
b=vpa(sol.b,4)
c=vpa(sol.c,4)
d=vpa(sol.d,4)
  3 Comments
Birdman
Birdman on 6 Feb 2018
Edited: Birdman on 6 Feb 2018
Well, other way around is to take inverse of the matrix as stated in question and do the following:
syms a b c d
sol=[a;b;c;d]==vpa(inv([2 2 -7 2;3 2 -5 6;9 -8 1 -4;1 5 3 -1])*[5;-17;14;9],4)
By the way, it should work without an error if you have Symbolic Toolbox.
Or, just simply:
inv([2 2 -7 2;3 2 -5 6;9 -8 1 -4;1 5 3 -1])*[5;-17;14;9]
will give you a,b,c and d respectively.
xoxox
xoxox on 6 Feb 2018
Yes Thank you!

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More Answers (1)

Andrei Bobrov
Andrei Bobrov on 6 Feb 2018
A = [2 2 -7 -2
3 2 -5 6
9 -8 1 -4
1 5 3 -1];
b = [5;-17;14;9]
abcd = A\b;

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