Using the pythagorean theorem a^2+b^2=c^2, we can say that 3^2+b^2=10^2.
Simplify and you get 9+b^2=100. Subtract 9 from both sides and you get b^2=91. When you take the square root you get 9.53939... round to the nearest tenth and the missing side is 9.5.
