From Longman Dictionary of Contemporary Englishuse your imaginationuse your imaginationspokenGUESS used to tell someone that they can easily guess the answer to a question, so you should not need to tell them → imagination
Examples from the Corpus
use your imagination• Of course, Vincent explained to Theo, he could avoid the expense of models and use his imagination.• This means using your imagination and buying some fairly unusual items.• We also need to encourage children to use their imaginations in science lessons.• When the information was slow in coming, the announcers were forced to use their imaginations to fill in the details.• This would be a well-placed lesson to her in how to use her imagination a bit more.• With Game Boys and other computers you don't need to use your imagination.• How can you look at a bunch of stars, so far away, and so incomprehensible, without using your imagination? 