A. $\int_{\alpha}^{\beta} [P(\varphi(t), \psi(t))+ Q(\varphi(t), \psi(t))] \varphi'(t)\, dt$
B. $\int_{\alpha}^{\beta} [P(\varphi(t), \psi(t))\varphi'(t)+ Q(\varphi(t), \psi(t))\psi'(t)] \, dt$
C. $\int_{\alpha}^{\beta} [P(\varphi(t), \psi(t))+ Q(\varphi(t), \psi(t))] \, dt$
D. $\int_{\alpha}^{\beta} [P(\varphi(t), \psi(t))+ Q(\varphi(t), \psi(t))] \psi'(t)\, dt$
设 f(x, y) 在曲线弧 L 上有定义且连续，L 的参数方程为 {x=varphi(t) y=psi(t) f(varphi(t), psi(t)), dt
设函数 varphi(x) 连续，且满足 varphi(x)= e^x + int_0^x t varphi(t), dt - x int_0^x varphi
5.(单选题) 设 z = varphi(x + y) + psi(x - y), 则必有()A. $z_{xx}^{\prime\prime} + z_{yy
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(25) int (cos )^2(omega t+varphi )dt;
(25) int (cos )^2(omega t+varphi )dt;
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摆线{}x=a(t-sin t)y=a(1-cos t)dtA. $\int_{0}^{2\pi a}\pi a^{2}(1-\cos t)^{2}d[a(t-