I'm not sure in what context you are phrasing this. I'm going on the assumption that you are referencing the trial proceeding of Jesus before the High Priest:
"But Jesus held his peace, And the high priest answered and said unto him, I adjure thee by the living God, that thou tell us whether thou be the Christ, the Son of God.
Jesus saith unto him, Thou hast said: nevertheless I say unto you, Hereafter shall ye see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.
Then the high priest rent his clothes, saying, He hath spoken blasphemy; what further need have we of witnesses? behold, now ye have heard his blasphemy." - Matthew 26:63-65
From what I've heard, when the High Priest adjures one to answer, that person is under obligation under the Jewish law to answer truithfully. The response Jesus gives, "Thou hast said" is a colloquialism of that day that is in the affirmative. An equivilent response is found in the parallel passage in Mark 14:61-63, "...Again the high priest asked him, and said unto him, Art thou the Christ, the Son of the Blessed? And Jesus said, I am: and ye shall see the Son of man sitting on the right hand of power, and coming in the clouds of heaven. Then the high priest rent his clothes, and saith, What need we any further witnesses?"
Here it is the very definite answer, "I am".