To find the restrictions you need to set the denominator equal to zero and solve the equation (The solution or solutions are the restricted values.)
In this case we need to solve:

x^2-3x-10 = 0

and

x^2-8x+15 = 0

The solutions for

x^2-3x-10 = 0 are x1 = 5 and x2 = -2

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The solutions for

x^2-8x+15 = 0 are x1 = 5 and x2 = 3

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The restrictions on the variable are x needs to be other than -2, 3 and 5.