I solved it. I forget to use np.dot()

The reason it fails is that you have *not* used the correct formula. â€ś*â€ť means â€śelementwiseâ€ť multiply, but you need dot product style multiply there. My guess is that you just need an explanation of the notation that Prof Ng uses for multiplication. Hereâ€™s a thread which goes through all that in detail. Please have a look and let us know if any further questions after reading that.

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Thank you so much. That was a great explanation.