Answer:
x= √(10/25)
Explanation:
From what you've written, you're on the right track. The formula is a^2+b^2=c^2. our two sides are a and b (doesn't really matter here which is which). And the hypotenuse, the longest leg the diagonal, is always c. Based on your substitution, everything is correct, except x. x should be squared. so the equation you should have is (1/5)^2 + (3/5)^2=x^2. From there, solve for x by adding a^2 and b^2 to get 10/25 = x^2.
Take the square root of each side to find √(10/25)=√(x^2). This is simplified as x equals plus or minus √(10/25). it's plus or minus because you took the square root. It's important to write that when solving square root. However, since this is a triangle your answer will be positive(you can't have negative distance).