√(√10² + √6²) = √(10 + 6) = √16 = 4 (if the two given sides are both legs)

or √(√10² - √6²) = √(10 - 6) = √4 = 2 if the √10 was the hypotenuse

Pos 1 assumes sqrt(10) is the hypotenuse. x=sqrt(10-6)=sqrt(4)=2

Pos 2 assumes x is the hypotenuse. x=sqrt(10+6)=sqrt(16)=4