Is it right to repeat prayer with the same content?
Absolutely!
Luke 18:1-8 New International Version (NIV)
The Parable of the Persistent Widow
18 Then Jesus told his disciples a parable to show them that they should always pray and not give up. 2 He said: “In a certain town there was a judge who neither feared God nor cared what people thought. 3 And there was a widow in that town who kept coming to him with the plea, ‘Grant me justice against my adversary.’4 “For some time he refused. But finally he said to himself, ‘Even though I don’t fear God or care what people think, 5 yet because this widow keeps bothering me, I will see that she gets justice, so that she won’t eventually come and attack me!’”
6 And the Lord said, “Listen to what the unjust judge says. 7 And will not God bring about justice for his chosen ones, who cry out to him day and night? Will he keep putting them off? 8 I tell you, he will see that they get justice, and quickly. However, when the Son of Man comes, will he find faith on the earth?”
Hint: “his chosen ones, who cry out to him day and night? Will he keep putting them off? I tell you HE WILL SEE THAT THEY GET JUSTICE, AND QUICKLY.” (all caps mine)
As well as
1 Thessalonians 5:16-18 New International Version (NIV)
16 Rejoice always, 17 pray continually, 18 give thanks in all circumstances; for this is God’s will for you in Christ Jesus.
yes, we need pray until God answer our prayer.
Luke 11:9-13 New King James Version (NKJV)
Keep Asking, Seeking, Knocking
9 “So I say to you, ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. 10 For everyone who asks receives, and he who seeks finds, and to him who knocks it will be opened. 11 If a son asks for [a]bread from any father among you, will he give him a stone? Or if he asks for a fish, will he give him a serpent instead of a fish? 12 Or if he asks for an egg, will he offer him a scorpion? 13 If you then, being evil, know how to give good gifts to your children, how much more will your heavenly Father give the Holy Spirit to those who ask Him!”