Please use " ^ " to denote exponentiation:
f(x) = –(x + 8)^2 – 1
Find the first derivative: f '(x) = -2(x+8)(1)
Set this = to 0: -2(x+8) = 0
solve for x: x = -8
Divide the number line into subintervals based upon x=-8:
(-inf, -8) and (-8, inf)
Choose a test value for x from each interval, e. g., -10 from the first interval and 20 from the second.
Subst. this test value into the derivative, shown above.
If the result is + the function is incr on that interval; if - the fn. is decr.
Questions welcome!