Length of Diagonal of Unit Square
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Theorem
The length of a diagonal of a square of side length $1$ is $\sqrt 2$) (the square root of $2$).
Proof
Two adjacent sides $AB$, $BC$ and the diagonal $AC$ of square $ABCD$ form a right triangle.
The hypotenuse of triangle $\triangle ABC$ can be found by using Pythagoras's Theorem:
- $AC^2 = AB^2 + BC^2$
from which:
- $AC^2 = 2$
and so:
- $AC = \sqrt 2$
$\blacksquare$
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $1 \cdotp 41421 \, 35623 \, 73095 \, 04880 \, 16887 \, 24209 \, 69807 \, 85697 \ldots$
- 1993: Richard J. Trudeau: Introduction to Graph Theory ... (previous) ... (next): $2$. Graphs: Paradox
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $1 \cdotp 41421 \, 35623 \, 73095 \, 04880 \, 16887 \, 24209 \, 69807 \, 85697 \ldots$