問題：次の式を計算せよ
- (1) \( \displaystyle \int_{}^{} 3x(x^2 + 7) \, dx \)
- (2) \( \displaystyle \int_{}^{} \dfrac{2x}{x^2 + 3} \, dx \)
- (3) \( \displaystyle \int_{}^{} \sin^5 x\cos x \, dx \)
- (4) \( \displaystyle \int_{-1}^{0} x^3e^{2x^4 - 2} dx \)
- (5) \( \displaystyle \int_{0}^{9} \dfrac{x}{\sqrt{81 - x^2}} \, dx \)