not a right triangle
We can use the Pythagorean theorem to see if it is a right triangle
a^2 + b^2 = c^2
15^2 + 12^2 = 21^2
225 + 144 = 441
369 = 441
This is not true so it is not a right triangle
A triangle is a right angled triangle if sum of squares of two sides is equal to the square of third side.
it is not a right angled triangle.
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Mathematics, published 11.05.2023
Mathematics, published 23.03.2023