Pythagorean Theorem: [tex]\sqrt{a^{2} * b^{2}} = c^{2}[/tex]
In this problem, only sides b and c are given. In this situation, since we want to find a, it's:
[tex]a^{2} = \sqrt{c^{2} - b^{2}}[/tex]
[tex]a^{2} = \sqrt{10^{2} - 9^{2}}[/tex]
[tex]9^{2} = 81\\10^{2} = 100[/tex]
After given squared numbers are solved, now we solve for a:
[tex]a^{2} = \sqrt{100 - 81}[/tex]
[tex]a^{2} = \sqrt{19}[/tex]
a = 4.358 . . . :)
