Trying to find if three inputed numbers can make a right triangle

Question

Kim 2015-10-24

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https://ww2.mathworks.cn/matlabcentral/answers/250779-trying-to-find-if-three-inputed-numbers-can-make-a-right-triangle

评论： Star Strider 2015-10-24

Can anyone help? I am trying to see if an array of three numbers inputted by a user can form a right triangle. My code is below and I can't figure out why it won't work. Thank you in advance!

sides =input('please enter 3 whole numbers in brackets []  :  ');
Sides =  perms(sides);% generate an array of the permutations of the input
Triange=0% initiate count
for a = 1:3
       for b = 1:3
            for c = 1:3
                  if (Sides(:,a)^ 2)+ (Sides(:,b)^ 2) ==  (Sides(:,c) ^ 2); 
                  Tri(:,:) = [Sides(:,a),Sides(:,b),Sides(:,c)];
                  Triangle=Triangle +1
                  else disp('there are no right triangles')
                  end 
              end% for c
         end% for b
  end%for a

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Answer 1

Star Strider 2015-10-24

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https://ww2.mathworks.cn/matlabcentral/answers/250779-trying-to-find-if-three-inputed-numbers-can-make-a-right-triangle#answer_197189

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It is difficult for me to follow your code. I would do it this way:

sortsides = sort(sides);
istri = sum(sortsides(1:2)) >= sortsides(3);                            % Will The 3 Numbers Form A Triangle?
isrightri = sum(sortsides(1:2).^2) == sortsides(3).^2;                  % Is It A Right Triangle?
if isrightri
    fprintf('\n\tThe numbers {%d, %d, %d} form a right triangle.\n', sortsides)
elseif istri && ~isrightri
    fprintf('\n\tThe numbers {%d, %d, %d} do not form a right triangle.\n', sortsides)
elseif ~istri
    fprintf('\n\tThe numbers {%d, %d, %d} do not form any triangle.\n', sortsides)
end

The ‘sortsides’ assignment sorts the sides in ascending order. This is important for the efficiency of the code! If the sum of the lengths of the two shorter sides is greater that the length of the third side, then you can form a triangle (the istri assignment), otherwise it is impossible to form any triangle from them. Then determine if it is a right triangle, using the Pythagorean Theorem.