As shown in the figure, in the cube ABCD - a'b'c'd ', find the cosine value of the dihedral angle a' - bd-a

As shown in the figure, in the cube ABCD - a'b'c'd ', find the cosine value of the dihedral angle a' - bd-a

&As shown in the figure, connect AC, intersect BD with P, connect a & # 39; P, then the cosine value of AC ⊥ BD, ∵ AA & # 39; ⊥ planar ABCD, ∵ AA & # 39; ⊥ BD, ∵ BD ⊥ planar AA & # 39; C ∵ BD ⊥ a & # 39; P, ∵ APA & # 39; is the cosine value of dihedral angle A & # 39; - bd-a; if the side length of the cube is 2, then AP = root 2, ∵ AA & # 39

（a2-4/a2-4a+3）×（a-3/a2+3a+2=?

The original formula = [(a-178; - 4) / (a-178; - 4A + 3)] × [(A-3) / (a-178; + 3A + 2)]
={(a-2)(a+2)/[(a-1)(a-3)]}×{(a-3)/[(a+1)(a+2)]}
=(a-2)/[(a-1)(a+1)]

Let a (1,2) B (- 3,3) be the minimum of PA + Pb if P is on the x-axis

First, find out the symmetric point of B as B ', then find out the point of X axis of b'a intersection as P. the final answer can be obtained by using the formula of distance between two points

Can 3.6 × 4.8-3.8 be calculated simply?

I don't think the original formula can be simplified

It is known that the side area of the cone is 15 π cm and the generatrix length is 5 cm

The side area of the cone has the formula s = 1 / 2L × R, l is the circumference of the bottom circle, R is the length of the generatrix, we can know that l = 6 π, then the radius of the bottom circle is r = 3, so the area of the bottom circle is 9 π, and the total area is 15 π + 9 π = 24 π

Please have 8 numbers, 6 of which are: 0.51 (51 cycle), 2 / 3, 5 / 9, 0.51 (1 cycle), 24 / 47, 13 / 25,
If the fifth is 0.51 (1 cycle) in the order from small to large, then what is the third in the order from large to small?
If the fifth is 0.51 (51 cycle) in the order from small to large, then what is the third in the order from large to small?

Is it a wrong question? Is the fifth one 0.51 (cycle 51), or is the fourth one 0.51 (cycle 1), in that case, the third one is 13 / 25

Find the tangent equation at the intersection of y = x Λ 2 and circle 1 / 2x Λ 2 + 1 / 2Y Λ 2 = 1

Substituting y = x ^ 2 into x ^ 2 + y ^ 2 = 2, intersection a (1,1), B (- 1,1)
① Tangent of parabola: y '= 2x,
At a, K1 = 2, the tangent equation Y-1 = 2 (x-1), that is, y = 2x-1
At B, K2 = - 2, the tangent equation Y-1 = - 2 (x + 1), that is, y = - 2x-1
② Tangent of circle: x0 * x + Y0 * y = R ^ 2
The tangent equation x + y = 2 at a
The tangent equation at B is - x + y = 2

When a takes what kind of integer, the value of 100% of fraction a is an integer. When a takes what kind of integer, the value of 100% of fraction a is an integer

When a = 1,2,4,5,10,20,25,50 or 100, it satisfies the problem. If negative integers are considered, then a can also take the opposite of these nine numbers

Given that the system of equations 3x-4y = 129x + ay = B has infinite solutions, find a, B

Because the equations 3x -- 4Y = 12
9x+ay=b
There are infinitely many solutions,
So 3 / 9 = -- 4 / a = 12 / b
From 3 / 9 = -- 4 / A: a = -- 12,
From 3 / 9 = 12 / B, B = 36

(1) what is the quotient of the sum of 5 / 6 and its reciprocal minus 122?

(1) What's the quotient of the sum of 5 / 6 and its reciprocal minus 122?
122÷(5/6+6/5)
=122÷61/30
=60
(2) 40% of a number is 18 less than 60%. What's the number?
60%x-40%x=18
20%x=18
x=90