A piecewise function y = x (0 ＜ x ＜ 1) y = 0 (x = 1) y = 1 / 2 of negative x (x ＞ 1) why, when 0 ＜ x ＜ 1, that is, when 1 / X ＞ 1, why does f (1 / x) = negative x equal to - x, instead of 1 / 2 of negative x? 1 / X is greater than 1. Why is it not equal to 1 / 2 of negative x

A piecewise function y = x (0 ＜ x ＜ 1) y = 0 (x = 1) y = 1 / 2 of negative x (x ＞ 1) why, when 0 ＜ x ＜ 1, that is, when 1 / X ＞ 1, why does f (1 / x) = negative x equal to - x, instead of 1 / 2 of negative x? 1 / X is greater than 1. Why is it not equal to 1 / 2 of negative x

Yes, the third segment x > 1 is satisfied, so y = 1 / X (x > 1) is satisfied
But the value of the variable is 1 / X; so f (1 / x) = minus 1 / x, 1 / 2 = - X

Find the maximum or minimum value (1) (- ∞, + ∞) (2) [1,3] of the function y = xsquare-4x + 1 in the following interval. Given that the function y = 1 / 2 of X + X, X belongs to [2,3], find the maximum and minimum value of the function y. if the image of the function f (x) = kxsquare-2x + 2 is above the x-axis, then the value range of K is___ The maximum value of y = root - x square - 5x + 6 is_________ If the maximum value of function f (x) = - x square + 4x in the interval [3, M] is m square - 5m + 7, then the value of M is () a1b4c1 or 5 / 4 D2 positive and negative root sign 13

(1) It is a parabola with an opening upward. Taking the minimum value at x = 2 - 3 (2) is a hook function, so at the two ends of X, y obtains the maximum value x = 3, y = 10 / 3 and the minimum value x = 2, y = 5 / 2 (3) respectively. It shows that there is no intersection point between the function and the X axis, then the discriminant 4-8k is less than 0, K belongs to [1 / 2, positive infinity] (4) what is the "root x square"

High school mathematics function problem solving and analysis
In △ ABC, the opposite sides of inner angles a, B and C are a, B and C respectively. It is known that a = 2, C = radical 2, cosa = - (radical 2) / 4
Find the value of sinc and B
Answer: sinc = (root 7) / 4. B = 1
Why can't b be equal to 2?

From cosine theorem, cosa = (C & # 178; + B & # 178; - A & # 178;) / 2BC
That is - (radical 2) / 4 = (b ^ 2 = 2-4) / 2 radical 2B
B ^ 2 + B-2 = 0
Cross phase multiplication (B + 2) (B-1) = 0
B = 1 or B = - 2 (rounding off)
Then Sina = radical (1-cos ^ 2b) = radical 14 / 4
Then the sine theorem is a / Sina = C / sinc
That is 2 / (radical 14 / 4) = radical 2 / sinc
So sinc = (root 7) / 4
So in the title, B is not equal to 2, only - 2

Senior high school mathematics function questions:
Answer:
Given the function f (x) + 2x squared - 9x - 4, and f (- a) = - 1, find the value of A
Find the domain of the function y = x square + 3x + 2 / 2 + root x + 2
I am too poor in mathematics, the problem can not be done, please help!
Thank you very much!
Hurry!

f(-a)=2a²+9a-4=-1
2a²+9a-3=0
a=(-9±√105)/4
Denominator X & # 178; + 3x + 2 ≠ 0
And the root sign is x + 2 ≥ 0
So x > - 2, X ≠ - 1