Seeking the great spirit in mathematical problems A is an acute angle, and cosa

Seeking the great spirit in mathematical problems A is an acute angle, and cosa

∵ when cosa = 1, a = 0, and a is an acute angle
∴0

For an irregular iron sheet as shown in the figure, the notch boundary is a part of a parabola with a width of 4 decimeters and a depth of 2 decimeters (the distance from the vertex to the straight line of a and B at both ends). First, the notch boundary should be cut into an isosceles trapezoid
(1) If the width of the notch remains unchanged, the minimum area of the trapezoidal notch after cutting is obtained

Can you give me a picture

If the fractional equation 1 / x + 1 = 2 / x + k about X has only positive solutions, then the value range of K is

Multiply by (x + 1) (x + k)
x+k=2x+2
x=k-2>0
k>2

If a and B are two events, prove that:
P(A \x05\x05\x05\x05\x05∩ B' )= P(A) - P(A \x05\x05\x05\x05\x05∩ B)
P(A\x05\x05\x05\x05\x05∪ B) = 1- P(A' \x05\x05\x05\x05\x05∩ B' )
The large space in the middle above can be ignored

&Nbsp; & nbsp; left = P (a cross B & # 39;) = P (a) * P (B & # 39;) = P (a) * (1-p (b)) & nbsp; & nbsp; right = P (a) - P (a cross b) = P (a) - P (a) * P (b) = P (a) * (1-p (b)) = the second question on the left is the same ~ to put it simply, P (a cross b) is replaced by P (a) * P (b) ~