Assertion: tetrahedron's angle | /r/HasProperty | acute
Facets:
Source sentences:
text: Simplifying we get $c^{2}=\sqrt{a^{2}+c^{2}}\sqrt{b^{2}+c^{2}}\cos\gamma,$ implying that $\cos\gamma\gt 0,$ meaning that $\gamma$ is less than $90^{\circ}.$ Because of the (cyclic) symmetry of the expressions involved, the other two angles are also acute.