2 by 1 / 3 + 3 by 1 / 4 + 4 by 1 / 5 +. + 49 by 1 / 50 =?

2 by 1 / 3 + 3 by 1 / 4 + 4 by 1 / 5 +. + 49 by 1 / 50 =?

The ratio of three sides of a triangle is 8:15:17, and the perimeter is 80cm. Find the area of the triangle
Be specific

The ratio of three sides of the triangle is 8:15:17, and the perimeter is 80cm
The three sides of the triangle are 16,30,34cm
According to Helen's formula, P = 80 / 2 = 40
Area of triangle = √ [40 * (40-16) (40-30) (40-34)]
=√33600
=40√21
=183.3cm^2

1 / 5 divided by (1-3 / 1 × 2 / 1)

1 / 5 divided by (1-3 / 1 × 2 / 1)
=1 / 5 divided by (1-1 / 6)
=1 / 5 divided by (5 / 6)
=1 / 5 times (6 / 5)
=6 out of 25

The diameter of a semicircle is 5 decimeters. How many decimeters is its perimeter and how many square meters is its area

Perimeter: 3.14 × 5 × 1 / 2 + 5
=7.85+5
=12.85 decimeters
Area: 3.14 × 2.5 × 2.5 × 1 / 2 = 9.8125 square decimeters

22.88 / 5.2 + 4.8 * 6.5 52.8-6 * 1.43 17.4-19.8 / 4.5 * [0.5 + 0.25] [using recurrence equation]

22.88/5.2+4.8×6.5
=4.4+4.8×6.5
=4.4+31.2
=35.6
52.8-6×1.43
=52.8-8.58
=44.22
17.4-19.8/4.5×[0.5+0.25]
=17.4-4.4×0.75
=17.4-3.3
=14.1

In △ ABC, ∠ a = 105 °, the angular bisector of ∠ ACB intersects AB at point D, and there is a point E on BC, connecting AE, ∠ CAE = 30 ° to find the degree of ∠ CDE

Tell you a good way, there is an answer, do not believe you look at this
Just change the number,

It is known that sample a is A1, A2, A3, and B is B1, B2, B3. If a1-b1 = A2-B2 = a3-b3, what is the relationship between the variance of sample a and sample B?
You need to prove your conclusion

If the sum of the upper and lower base of the isosceles triangle ABCD is 4, and the acute angle between the two diagonals is 60 degrees, the area of the isosceles trapezoid is 4 times the root sign 3

Not necessarily. Let's assume ab ‖ CD, if ∠ AOB = 60 °, then the answer is 4 times root sign 3, and the method is the same as above;
If ∠ AOD = 60 °, the answer is 4 / 3 root sign 3. The method is similar to

If the domain of F (x + 1) is [- 1,1], then the domain of F (lgx) is?

The two domains are connected by the domain of F (x)
Firstly, the domain of F (x) is obtained by the domain of F (x + 1)
Then the domain of F (lgx) can be obtained from the domain of F (x)
Let t = x + 1
-1

A snail, climbing a tree of 9m high, rises LM in the daytime and declines 13m at night. It starts to climb up one morning. How many days later can it reach the top of the tree?

(9-1) △ 1-13 + 1, = 8 △ 23 + 1, = 13 (days). A: you can reach the top of the tree after 13 days