English: Illustration for Fermat's right triangle theorem. One of the two right triangles shown has its two sides equal to the side and hypotenuse of the other one. According to the theorem, it is not possible for all four side lengths ${\displaystyle a\!\,}$, ${\displaystyle b\!\,}$, ${\displaystyle c\!\,}$, and ${\displaystyle d\!\,}$ to be integers. In this case ${\displaystyle a=3\!\,}$, ${\displaystyle c=4\!\,}$, ${\displaystyle d=5\!\,}$, and ${\displaystyle b={\sqrt {7}}\!\,}$.