请问二阶微分的符号如何判断？

请问二阶微分的符号如何判断？

老大，这个题目有问题？d^2(F(x,y,z）多了一个括号，3d^2代表什么呀，
按照一般理解，应该是




d

[
F(

x,y,z

)

]

2

=d(


x
2



)
+d(


y
2



)
+2dxdy


MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbWexLMBbXgBd9gzLbvyNv2CaeHbl7mZLdGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabauaaneaacaWGKbWaamWaaeaacaWGgbWaaeWaaeaacaWG4bGaaiilaiaadMhacaGGSaGaamOEaaGaayjkaiaawMcaaaGaay5waiaaw2faamaaCaaabeqaaiaaikdaaaGaeyypa0JaamizamaabmaabaGaamiEamaaCaaabeqaaiaaikdaaaaacaGLOaGaayzkaaGaey4kaSIaamizamaabmaabaGaamyEamaaCaaabeqaaiaaikdaaaaacaGLOaGaayzkaaGaey4kaSIaaGOmaiaadsgacaWG4bGaamizaiaadMhaaaa@5970@



把以上代码放在mathtype5.0以上版本中表示就可以了