Answer:
7√2
Explanation:
Remark
Draw another line parallel to 7.
Move to the other end of 3
that makes the vertical leg on the left 10 - 3 = 7
You now have a smaller right triangle.
Equation
a = 7
b = 7
c = x
Solution
x^2 = 7^2 + 7^2
x^2 = 49 + 49
x^2 = 98
x^2 = 7 * 7 *2
sqrt(x^2) = sqrt(7 * 7 * 2)
The rule about square roots is for every pair of factors you can take one out of the square root sign and throw the other one away.
x = 7 sqrt(2)