



 
Hi Amanda. The derivative of f evaluated at x=21 will tell you the slope at that point. if f(x) = sqrt(x+4), then f'(x) = 1 / [ 2 (sqrt(x+4) ]. Thus f'(21) = 1 / [ 2 (sqrt(21+4) ] = 1 / 10. If 1 / 10 = 1 / n , then n is 10, and that is indeed an integer. Cheers,  


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