Answer:
x = 4
Step-by-step explanation:
Using Pythagoras' identity in the right triangle.
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
x² + 1² = 9²
x² + 1 = 81 ( subtract 1 from both sides )
x² = 80 ( take square root of both sides )
x = =
=
×
= 4