Question 177391
You're on the right track, I'll start where you left off.



{{{a^2+1=5}}} Start with the given equation.



{{{a^2=5-1}}} Subtract 1 from both sides.



{{{a^2=4}}} Combine like terms.



{{{a=sqrt(4)}}} Take the square root of both sides. Note: we're only taking the positive square root.



{{{a=2}}} Take the square root of 4 to get 2



So the solution is {{{a=2}}} which means that the missing side length is 2 units.