计算定积分∫(-1,1) [(2+(x^2)*(sin^2011)*x)/√(4-x^2)dx]
2个回答

∫(-1,1) [(2+(x^2)*(sin^2011)*x)/√(4-x^2)dx]

=∫(-1,1) 2/√(4-x^2)dx+∫(-1,1)(x^2)*(sin^2011)*x)/√(4-x^2)dx]

=∫(-1,1) 2/√(4-x^2)dx

因为 (x^2)*(sinx)^2011/√(4-x^2) 是奇函数,而奇函数在对称区间是的定积分等于0,

令x=2sint,dx=2costdt,

=∫ (-1,1)2/√(4-x^2)dx

=2∫ (0,1)2/√(4-x^2)dx

=∫(0,1) 8cost/√(4-4(sint)^2)dt

=∫(0,1)4cost/costdt

=(0,1)4t=4

所以原积分=4.