![\huge \boxed{\mathbb{QUESTION} \downarrow}](https://img.qammunity.org/2022/formulas/history/college/1jyfph24cxomkgaamjtwx4vsi2y95urtq7.png)
![\large \boxed{\mathbb{ANSWER\: WITH\: EXPLANATION} \downarrow}](https://img.qammunity.org/2022/formulas/engineering/college/8yws292u960at9h6j4zwjb6g91x4276wx6.png)
To solve these type of problems you need to use the pythagoras theorem ⇨ Hypotenuse² = Base² + Altitude².
Here,
- Altitude = 21 km.
- Base = 20 km
- Hypotenuse = c.
Now, let's solve for c.
Hypotenuse² = Base² + Altitude²
c² = (20)² + (21)²
c² = 400 + 441
c² = 841
c = √841
c = 29.
So, the value of c is 29 km.
NOTE :-
- Pythagoras theorem can be used only in the cases of right-angled triangles. Here, it's given that the triangle is right angled so we can use this theorem.