Given:
Height of right triangle = 9 mi
Hypotenuse = 17.5 mi
Base of right triangle = Distance across lake
To find:
The distance across the lake.
Solution:
Using Pythagoras theorem:
In right triangle, square of the hypotenuse is equal to the sum of the squares of the other two sides.
Subtract 81 from both sides.
Taking square root on both sides.
⇒ base = 15
The distance across the lake 15 mi.