A cone is a plane and a surface?

A cone is a plane and a surface?

Cone --- bottom --- plane, --- side --- surface

How many faces does a cone have? How many planes? How many surfaces

Two faces, a surface and a plane

When x = 1 is, the value of the algebraic expression PX & sup3; + QX + R is 9
When x = - 1, find the value of the algebraic expression PX & sup3; + QX + R + 9

When x = 1, the value of the algebraic expression PX & sup3; + QX + R is 9
p+q+r=9
When x = - 1,
px³+qx+r+9
=-p-q+r+9
=-(p+q+r)+2r+9
=-9+2r+9
=2r

Solving the plane equation of straight line (x-1) / 2 = y + 2 = (Z-3) / - 2 and point P (2,0,1)

Because the plane passes through the straight line (x-1) / 2 = y + 2 = (Z-3) / (- 2), and,
So let K [(x-1) / 2 - (y + 2)] + m [(y + 2) - (Z-3) / (- 2)] = 0,
Substituting x = 2, y = 0, z = 1, we get k [(2-1) / 2 - (0 + 2)] + m [(0 + 2) - (1-3) / (- 2)] = 0,
It is reduced to 2m-3k = 0,
Taking M = 3 and K = 2, the plane equation obtained is 2 [(x-1) / 2 - (y + 2)] + 3 [(y + 2) - (Z-3) / (- 2)] = 0,
It is reduced to 2x + 2Y + 3z-7 = 0

4AB - 8a, B do it by factorization
Yes, write down the process

4ab^2-8a^2b=4ab(b-2a)

As shown in the figure, in the cube abcd-a1b1c1d1, the tangent of the dihedral angle b-a1c1-b1 is___ ．

Using the vector method, the solution is as follows: take D1 as the origin, d1a1 as the X axis, d1c1 as the Y axis, d1d as the Z axis, establish the d1-xyz space rectangular coordinate system

The natural numbers 1 ~ 100 are arranged in the following table
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
.
99 100
If the sum of the six numbers in the box is 327, what is the smallest of the six numbers?
8.14 pm before 9:30!

Let the first number be x, then the second number be x + 1, the third x + 2, the fourth x + 7, the fifth x + 8 and the sixth x + 9
So x + (x + 1) + (x + 2) + (x + 7) + (x + 8) + (x + 9) = 327
X=50

Given the set a = {X-2 ≤ x < a}, B = {y y = 2x + 3, X ∈ a}, C = {Z Z = x ^ 2., X ∈ a}, and C is contained in B, the value range of a is obtained

You can draw the set B and C in the plane coordinate system. The intersection of the positive half axis of X is (3,9), and the intersection of the negative half axis is (- 1,1)
Because C is contained in B, under the premise of X, the ordinate value of set C is smaller than that of B,
So, - 1 ≤ a ≤ 3

3.5x + 3.5 × 5 = 33.25

3.5x + 3.5 × 5 = 33.25 divided by 3.5
x+5=9.5
x=9.5-5
x=4.5

Is it right that the sum of squares of two diagonals of a parallelogram is equal to the sum of squares of four sides?

Using vector to prove the simplest, only 3 steps, and do not make any auxiliary line
(the following quantities represent vectors, but the arrow can't be typed.)
Proof: parallelogram ABCD
AC＝DC－DA
BD＝DA＋DC
So AC ^ 2 + BD ^ 2 = (dC-dA) ^ 2 + (DA + DC) ^ 2
＝DC^2＋DA^2－2DC*DA＋DC^2＋DA^2＋2DC*DA
＝AB^2＋BC^2＋CD^2＋DA^2
It is known that: (AC ^ 2 + BD ^ 2) / 2 = AB ^ 2 + BC ^ 2