prior information

[Isbell]

Could you help me to correct the following sentence?

Often, we need to have some prior information before we solve the question. (e.g. we need to know that the range of the function y=e^x is always greater than zero in Mathematics point of view.)

[Beeesneees]

My suggestion:
Often, we need to have some prior information before we can solve a question (e.g. we need to know that the range of the function y=e^x is always greater than zero from a mathematical point of view).
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[Isbell]

Thanks a lot, Beeesneees. One more question :-)
"We must have some prior information before we can solve a question." Does this sound more "definite"? Or what's your suggestions to make the statement so that it'll carry its weigh even more??? I mean, I kind of need a "forceful" tone there......

[Thredder]

Often, before we can solve a question, some prior information is required.

[Isbell]

Thanks, Thredder.