Bonjour j'ai un devoir de math qui est sur la géométrie et c'est très difficile pour moi c'est niveau 3eme et je ne comprends rien.

assuming you mean addition: addition and subtraction are reverse operations.

step-by-step explanation:

step-by-step explanation:

this can be solved first with pythagorean theorem, which tells us to square both legs of the triangle and sum it. this will be equal to the square of the hypotenuse.

the hypotenuse is the side "opposite" the 90 degree angle, which is x.

so we can write using pythagorean theorem,

simplifying:

to further simplify this radical, we need to use the property  

thus