Andika Theorem ya Pythagoras.

Theorem ya Pythagoras inasema kwamba katika pembetatu mraba, jumla ya miraba ya pande mbili fupi (miguu) ni sawa na mraba wa upande mrefu zaidi (hypotenuse).

$$a^2 + b^2 = c^2$$

Ambapo $a$ na $b$ ni urefu wa miguu, na $c$ ni urefu wa hypotenuse.

Kutoka kwenye picha, tuna:
Hypotenuse $c = 20 \text{ cm}$
Mguu mmoja $a = 16 \text{ cm}$
Mguu mwingine $b = P$ (upande tunaotafuta)

Hivyo, tunapata:

$$(16 \text{ cm})^2 + P^2 = (20 \text{ cm})^2$$

Kwanza, hesabu miraba ya namba zinazojulikana:

$$256 \text{ cm}^2 + P^2 = 400 \text{ cm}^2$$

Toa $256 \text{ cm}^2$ kutoka pande zote mbili za mlinganyo:

$$P^2 = 400 \text{ cm}^2 - 256 \text{ cm}^2$$ $$P^2 = 144 \text{ cm}^2$$

Pata mzizi wa mraba wa pande zote mbili ili kupata $P$:

$$P = \sqrt{144 \text{ cm}^2}$$ $$P = 12 \text{ cm}$$

Urefu wa upande $P$ ni $\boxed{\text{12 cm}}$.