A surveyor measures the distance across a straight river by the following method: Starting directly across from a tree on the opposite bank, he walks x = 108 m along the riverbank to establish a baseline. Then he sights across to the tree. The angle from his baseline to the tree is θ = 37.4°. How wide is the river?

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.