圓體積

圓方程：x²+y²=r²

體積：π∫^r_-ry²dx

=π∫^r_-r[r²-x²]dx

=π[r²x-x³/3]^r_-r

=π{[r³-r³/3]-[r²(-r)-(-r)³/3]}

=π{2r³/3+r³-r³/3}

=4πr³/3

∴圓體積=4πr³/3