Question 528213
Use an inverse trigonometric function to write theta as a function of x. There is a sketch of a right triangle with 10 as the opposite side, (x+1) as the adjacent, and theta as the hypotnuse/opposite angle. 
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If I interpret your directions properly,
tan(theta) = (x+1)/10
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theta = invtan[(x+1)/10]
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Cheers,
Stan H.