Answer:
2
Step-by-step explanation:
Since this is a right triangle, we can use the Pythagorean theorem
a^2 +b^2 = c^2 where a and b are the legs and c is the hypotenuse
a^2 + (2.1)^2 = (2.9)^2
a^2 +4.41=8.41
a^2 = 8.41-4.41
a^2 =4
Take the square root of each side
sqrt(a^2)=sqrt(4)
a=2
