using Pythagoras theorem which says that the square of the hyponeneus side of a right angled triangle is equal to the sum of square of the two opposite sides.
mathematically,
|H|² = |OPP|² + |ADJ|²
H= (x-2) , opp= 9 adj=(x+1)
(x-2)² = (9)² + (x+1)²
x² -4x + 4 = 81 + x²+2x+1
collecting the like terms
x²- x² - 4x-2x = 81 +1 - 4
- 6x = 89 -4
-6x = 78
divide both sides by the coefficient of x which is -6
