q = Integrate[ Integrate [ 1,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^2,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2y,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^3,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^4,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2y^2,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^4,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^4y,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2y^3,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^5,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^6,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^4y^2,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ x^2y^4,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]

q = Integrate[ Integrate [ y^6,{ y, 0, Sqrt[1-x*x]} ], {x, -1, 1 }]
N[q,20]