$\int_{0}^{\infty} e^{-x^2}\cos (2bx)dx=\frac{\sqrt{\pi}}{2}e^{-b^2}$ Cho tích phân $$\int_{0}^{\infty}e^{-x^2}dx=\frac{\sqrt{\pi}}{2}$$ Chứng minh rằng $$\int_{0}^{\infty} e^{-x^2}\cos (2bx)dx=\frac{\sqrt{\pi}}{2}e^{-b^2}$$ [RIGHT][I][B]Nguồn: MathScope.ORG[/B][/I][/RIGHT] __________________ |