The maximum value of quadratic function y = - 2x2 + 4x-9 is () A. 7B. -7C. 9D. -9 | Math enthusiast | Mathematical art

The maximum value of quadratic function y = - 2x2 + 4x-9 is () A. 7B. -7C. 9D. -9

According to the formula: ∵ a = - 2 ＜ 0, ∵ y = - 2x2 + 4x-9, the opening of the image is upward, and there is a maximum, ∵ ymax = 4ac − b24a = 4 × (− 2) × (− 9) − 16 − 2 × 4 = - 7

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