Graph the function y = 2x3 – x2 – 4x + 5. To the nearest tenth, over which interval is the function decreasing?

Differentiate the function: y′ = 6x² − 2x − 4 = 2(3x + 2)(x − 1). The derivative is negative between its zeros, x = −2/3 ≈ −0.7 and x = 1, so the function is decreasing on (−0.7, 1). The correct choice is C, (−0.7, 1).

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