The answer for this question is D, 2[tex] \sqrt{5} [/tex]
We can see that this triangle is a right triangle (because of the box on one of it's angles). In a right triangle, we know that, with a and b being the legs, and c being the hypotenuse, that a² + b² = c². In this case, x is the length of the hypotenuse and [tex] \sqrt{10} [/tex] is the value of both legs.
[tex] \sqrt{10} [/tex]² = 10, and x² = x², meaning that
10 + 10 = x²
x² = 20
To find what x is equal to, we take the positive square root of 20 (the length of a side can't be negative).
x = [tex] \sqrt{20} [/tex]
Now, we can simplify. [tex] \sqrt{20} [/tex] = [tex] \sqrt{2²*5} [/tex] (that's the prime factorization). But, since we see the number 2 two times in this square root, we can factor it out. The simplified form of our answer is:
2[tex] \sqrt{5} [/tex]
