問題：次の関数を計算せよ。
- (1) \( \displaystyle \int_{-1}^{1} (x^2 + 3) dx \)
- (2) \( \displaystyle \int_{-1}^{1} (x^3 - 5x) dx \)
- (3) \( \displaystyle \int_{-1.5}^{1.5} (5x^4 + 4x^3 - 3x^2 + 2x + 1) dx \)
- (4) \( \displaystyle \int_{-\pi}^{\pi} \{(x^3 + 2x)\sin^2x\} dx \)
- (5) \( \displaystyle \int_{-1}^{1} \dfrac{x - 1}{x^2 + 1} dx \)