Pick a relationship, choose which variable to solve for, and set the two knowns. The triangle covers the one you want, the equation rearranges itself, and the unit check shows the units combining into the answer.
Relationship
Solve for
Rearranged equation
F = m × a
Answer
F = 10.00 N
kg × m/s² = N
m2.0 kg
a5.0 m/s²
The triangle only works for the shape A = B × C. Cover the top and you multiply the two below; cover a bottom cell and you divide the top by the other. That is why relationships like v² = u² + 2as can’t be squeezed into a triangle.