f(x)=1/(5x^2+4)
f(x) = (5x^2 + 4)^-1 f'(x) = -(5x^2 + 4)^-2 (10x) = -10x(5x^2 + 4)^-2 f''(x) = -10x(-2)(5x^2 + 4)^-3 (10x) - 10(5x^2 + 4)^-2 = -10(5x^2 + 4)^-3 [ 10x^2 + 5x^2 + 4 ] can you set this equal to zero and solve? check my arithmetic.
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