For this problem you must do Pythagorean theorem:
[tex]a^{2} + b^{2} =c^{2}[/tex]
In this example 10ft is c and 7ft is a (or it could be b, and you'll be solving for a instead of b. It's the same thing, since a and b are both legs)
Plug what you know into the equation:
[tex]7^{2} +b^{2} = 10^{2}[/tex]
49 +b^{2} = 100
Bring 49 to the right side by subtracting it:
b^{2} = 51
Now you still must isolate b. The opposite of squaring is taking the square root so take the square root of both sides to cancel it from the left side:
[tex]b =\sqrt{51}[/tex]
b = 7.1414
b ≈ 7 ft
Hope this helped!
