(1 / 6-2 / 3 + 3 / 7) * - 42

(1 / 6-2 / 3 + 3 / 7) * - 42

simple form
=-1/6*42+2/3*42-3/7*42
=-7+28-18
=3
Excuse me, correct one question:
simple form
=-(240-1)/24-18
=-(240/24-1/24)-18
=-10+1/24-18
=-32+1/24
=-23 / 27 / 24

1. Given the complete set u = R, let the domain of function y = LG (x-1) be set a, and the domain of function y = be set B, then a ∩ (cub)=
2. Given sin θ =, and sin θ - cos θ > 1, then sin 2 θ=
2. Given that sin θ = 4 / 5 and sin θ - cos θ > 1, then sin 2 θ=

1. Empty set. The range of function, that is, b set is all real numbers, its complement is empty set, and any intersection with empty set is empty set
2. From sin θ - cos θ > 1, and the sine value must be less than 1, so the cosine value can only be less than 0, so sin2 θ = 2Sin θ * (- √ 1-sin θ * sin θ)

Cut a 1 cm square from the four corners of a 1 decimeter square, and the perimeter of the figure is () decimeter
The bottom area is 12.56 square decimeters, and its height is () decimeters

Question 1: perimeter unchanged, or 4 decimeters
Question 2: cylinder and cuboid: H = V / S = 12.56 / 12.56 = 1 (DM)
Cone: H = 3V △ s = 3 × 12.56 △ 12.56 = 3 (DM)

How to make up 24 kinds with 2, 3, 5, 6, 4 arithmetic and bracket

1:(2 - 3 + 5) × 6
2:(2 - (3 - 5)) × 6
3:2 × 3 × 5 - 6
4:(3+5)÷2×6

Let the sum of the first n terms of a sequence an be Sn, and (3-m) Sn + 2man = m + 3, where m is a constant and M is not equal to - 3, it is proved that an is an equal ratio sequence

（3-m）Sn+2m*an=m+3
(3-m)S(n-1)+2m*a(n-1)=m+3
simultaneous equation.
The solution is: an / a (n-1) = 2m / (3 + m)

A square surrounded by iron wire, the side length is 15.7 cm. Now use this iron wire to form a circle, the area of this circle is () square cm

15.7x4 = 62.8cm
62.8 ﹣ 3.14 ﹣ 2 = 10 cm
3.14x10x10 = 314 square centimeter

1 / 2 + 3 / 4 + 7 / 8 + 15 / 16 (simple)

1 / 2 + 3 / 4 + 7 / 8 + 15 / 16 (simple)
= 1/2 + 3/4 + 7/8 + 15/16
= ( 8+12+14+15) /16
= 49 /16

If the average of data x1, X2, X3, xn is x, then (x1-x) ^ 2 + (x2-x) ^ 2 +. + (xn-x) ^ 2 =?

This is the definition of mean and variance in a sample
The square of variance is generally defined as s ^ 2 = (x1-x) ^ 2 + (x2-x) ^ 2 +. + (xn-x) ^ 2
These two values generally have nothing to do with each other

Given that the length of the diagonal of a square is l, find its perimeter and area

∵ in a square, the length of diagonal line = L, the length of side = the length of diagonal line △ 2 = 22L, the area of square s = the square of side length = 12l2, and the perimeter C = 4 × side length = 4 × 22 = 22

Let f (x) be defined on (0, + ∞), f (1) = 0, derivative f '(x) = 1 / x, G (x) = f (x) + F' (x) (1) find the monotone interval and minimum value of G (x)

F '(x) = 1 / x, f (x) = LNX + C, because f (1) = 0, so C = 0, that is, f (x) = LNX, so g (x) = f (x) + F' (x) = LNX + 1 / XG '(x) = 1 / X-1 / x ^ 2 = (x-1) / x ^ 2 = 0, the unique stationary point x = 1. When x0, then G (x) monotonically decreases on (0,1); on (1, + ∞), G (x) monotonically increases. When x = 1, take the minimum g (1) = ln1 +