Question 971793
x^2 + ((2sqrt(105)^2)=2 (21^2 + 13^2)              2 * (square of one side+ square of adj side)=2 (square of each diagonal added)

x^2 + 4(105) = 2 *(441 +169)

x^2 +420 =1220

x^2=800
x=20 sqrt (2)