Ido not understand this question i don't know how to solve it me solve this question

Consider circle c with angle acb measuring 3/4 radians. if minor arc ab measures 9 inches, what is the length of the radius of circle c? if necessary, round your answer to the nearest inch.

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Let f(x) = 1/x^2 (a) use the definition of the derivatve to find f'(x). (b) find the equation of the tangent line at x=2