q = Integrate[ Integrate [ 1,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^2,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^4,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2y^2,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^4,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^6,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^4y^2,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2y^4,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^6,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^8,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^6y^2,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^4 y^4,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2 y^6,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^8,{ y, -Sqrt[1-x*x], Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]