#exodus 9:35 says that Pharaoh hardened his own heart. The Hebrew word for hardened in this verse is chezek, which also means to strengthen. The very next verse, 10:1, says that God hardened Pharaoh's heart. The Hebrew word for hardened in the 2nd verse is chabad, which also means to make heavy (as in important) or to glorify.

The implication is that Pharaoh resolved to defy God, so God encouraged him by inflating his ego, making him think that he might be able to get away with it.
#bo