Answer:
a = 2
Explanation:
To find the missing length we can use the Pythagorean theorem. Also, because it's a right triangle it makes it the perfect candidate!
The Pythagorean Theorem states:
a^2 + b^2 = c^2
Next, we substitute the letters with our given numbers (keep in mind that c is the hypotenuse which is the side facing the right angle)
a^2 + 2.1^2 = 2.9^2
Finally, we solve our equation (hint: use the calculator if needed)
a^2 = 4 (your answer is not final yet. You have to take the square root of both numbers)
a = 2 (Now that's the final answer!)