249

a)
410=400\cdot x^2
x^2=1{,}025
x=1{,}012422...\approx1{,}0124\ \left(tai\ x=-1{,}012422...\right)
b)
0{,}7x=1{,}2422...\%
x=1{,}7745...\%\approx1{,}77\%