真的被转晕了
你将 y = f(x, t) 抄错为 y = f(x, y);将 t = t(x, y) 抄错为 t = f(x, y),
F(x, y, t) = 0 抄错为 F(x, y, t)。已知条件全错,还能解答吗?
还是用印刷版原题提问为好!
解答如下:
y = f(x, t), t = t(x, y) 即 y = f[x, t(x,y)], 两边对 x 求导得
dy/dx = ∂f/∂x + (∂f/∂t)[∂t/∂x+(∂t/∂y)(dy/dx)]
则 dy/dx = [∂f/∂x + (∂f/∂t)(∂t/∂x)]/[1- (∂f/∂t)(∂t/∂y)] (1)
F(x, y, t) = 0, 则 ∂t/∂x = - (∂F/∂x)/(∂F/∂t), ∂t/∂y = - (∂F/∂y)/(∂F/∂t)
代入式(1), 得
dy/dx = [∂f/∂x - (∂f/∂t)(∂F/∂x)/(∂F/∂t)]/[1+ (∂f/∂t)(∂F/∂y)/(∂F/∂t)]
即 dy/dx = [(∂f/∂x)(∂F/∂t)-(∂f/∂t)(∂F/∂x)]/[(∂F/∂t)+(∂f/∂t)(∂F/∂y)]