Answer: 4 √ 14
Explanation:
Pythagorean theorem is (a^2 + b^2 = c^2)
Step 1. (10^2) + (x^2) = (18^2) {we divided the 20 by 2 to get one right triangle for the pythagorean theorem.}
Step 2. 100 + x^2 = 324
Step 3. x^2 = 224
Step 4. x ≈ 15 (rounded to the nearest whole number) (x = 14.9666295)
Step 5. Eliminate the wrong choices. B and D are both eliminated, because they are whole numbers, and they don't match the answer we got.
Step 6. Find the square root. 2 √ 106 is ≈ 20.59126, which isn't equal to our 14.966, .
Step 7. With all but one answer remaining, the answer would be 4 √ 14, and we can double-check. (14.9666295 = 14.9666295.)