2. Given that the function f (x) = 4x ^ 2-mx + 5 is an increasing function in the interval [- 2, positive infinity), then the value range of F (1) is a, ≥ 25B, = 25C, ≤ 25d, I don't understand why x = - B / 2A ≤ - 2, that is, M / 8 ≤ - 2, m ≤ - 16 Why is x = - B / 2A greater than or equal to - 2? | Math enthusiast | Mathematical art

2. Given that the function f (x) = 4x ^ 2-mx + 5 is an increasing function in the interval [- 2, positive infinity), then the value range of F (1) is a, ≥ 25B, = 25C, ≤ 25d, I don't understand why x = - B / 2A ≤ - 2, that is, M / 8 ≤ - 2, m ≤ - 16 Why is x = - B / 2A greater than or equal to - 2?

Draw a picture on the paper, make sure to draw a picture!
X = - B / 2a is his axis of symmetry
On the right side of the axis of symmetry are all increasing functions
So it's obvious that x = - B / 2a is to the left of - 2
So x = - B / 2A ≤ - 2
If x = - B / 2A ＞ - 2
So - 2 is on the left side of the axis of symmetry
Then (- 2, - B / 2a) is a decreasing function
So it doesn't conform to the meaning of the title
Do you understand?

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