Minti,
I would start by moving all the terms to one side of the equal sign.
1/4pi(x²) =10x x²(4pi)/8
1/4pi(x²)  10x + x²(4pi)/8 = 0
Now I see that there is a common factor of x so I get
x[1/4pi x  10 + x(4pi)/8] = 0
To eliminate the fractions I would multiply both sides by 8 and simplify to get
x[2pi x  80 + x(4pi)] = 0
x[2pi x  80 + 4x  pi x] = 0
x[(4  3pi) x  80] = 0
Thus
x = 0 or (4 3pi) x  80 = 0, that is
x = 0 or x = 80/(4  3pi)
Penny
