Two finite velocity triangles plus the speed-limit boundary show why gamma grows and then stops being finite. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Speed three gives gamma five fourths
The toy speed limit is 5 m/s. With speed 3 m/s, the quiet leg is 4 m/s, so beta is 3/5 and gamma is 5/4.
32+42=52γ=45
Speed four raises gamma to five thirds
Increasing only the speed to 4 m/s shrinks the quiet leg to 3 m/s. The denominator of gamma is smaller, so gamma becomes 5/3.
42+32=52γ=35
At speed five there is no finite gamma
At the speed limit, speed is 5 m/s and the quiet leg is 0 m/s. Gamma would divide by zero, so the checked boundary says no finite gamma.