The phrase "a complex problem that" is correct and usable in written English.
You can use it when introducing a specific issue or challenge that requires careful consideration or analysis.
Example: "The research team is currently addressing a complex problem that affects the entire ecosystem."
Alternatives: "a challenging issue that" or "a difficult situation that".
Analyzing the evolution of large and long-lived software systems is a complex problem that requires extensive tool support due to the amount and complexity of the data that needs to be processed.
"America must know that this is a complex problem that goes back 30 years".
Why? Cellulite is a complex problem that involves thin skin and the kind of fibrous bands holding in women's fat.
In a statement, YouTube said that identifying which video clips had been uploaded without permission was a complex problem that required the cooperation of the copyright owners.
But Carney, when asked what kind of measures the president had in mind, said: "It is a complex problem that will require a complex solution.
"It's a complex problem that will require a complex solution," the president's spokesman, Jay Carney, said in a news conference on Monday.
For Airbnb's part, in a blogpost on their website, German housing expert Daniel Hoffman says: "The tense housing market is a complex problem that is being driven by migration and a lack of new homes being built – not people sharing their homes through Airbnb".
Clearly, this is a complex problem that cannot be explained by any single factor or rubric.
A TranSTEP group will be convened when a problem owner identifies a specific, complex problem that needs resolution or action.
However, designing for low power adds an additional degree of complexity to an already complex problem that has historically targeted performance and area.
It is a very complex problem that includes illegal guns, a culture of violence, and sometimes a lack of problem solving skills....police definitely know who the gang members are, and anyone with even basic internet skills can find YouTube and Instagram accounts with photos of guns and drugs.
