How to solve the equation of 2 / x + 4 / x-80 = 100?

How to solve the equation of 2 / x + 4 / x-80 = 100?

2 / x + 4 / x-80 = 100
x/2+x/4-80=100
2x/4+x/4=180
3x/4=180
3x=180*4
3x=720
x=720/3
x=240

How to solve the equation that x divided by 1 and 2 / 7 equals 9 / 10?

X = 9 / 10 × 1 and 2 / 7
X = 1 and 11 out of 70

A rectangular sports field with an area of 100 square meters, if the width remains unchanged, and the length is doubled, what is the area of the enlarged sports field

2.1 divided by 7 equals 0.142857142857. What is the hundredth place after the decimal point? 142857 has six numbers 2 and a rectangle. If the width is unchanged and the length is increased by 6 meters, its area will increase by 54 square meters,

Vector a = (A1, A2, A3), B = (B1, B2, B3), then how are the point multiplication and cross multiplication of a and B expressed in coordinates?

Vector a · vector b = A1A2 + b1b2 + C1C2
Vector a × vector b = (b1c2-b2c1, c1a2-a1c2, a1b2-a2b1)

Compare the size of 2x and X & # 178; + 1 with the difference method
The size relation between 2x and X & # 178; + 1 when x = 2
2 the size of 2x and X & # 178; + 1 when x = 1
3 when x = - 1, the size of 2x and X & # 178; + 1
4 infer the size of 2x and X & # 178; + 1 when x goes to any real number
5. Generalize the size of 2x and X & # 178; + 1 when x, y go to any real number
Using the difference method

x²+x-2x=(x-1)²≥0
So: 2x ≤ X & # 178; + X
1 when x = 2, 2x

15. As shown in the figure, the line segments AB and DC represent the heights of buildings a and B respectively. Ab ⊥ BC, DC ⊥ BC, the elevation of point d measured from point B is, and the elevation of point d measured from point a is

(1) AE ⊥ CD through point a is at point E
According to the meaning of the title, ∠ DBC = ∠ α = 60 °, DGE = ∠ β = 30 °, AE = BC, EC = AB = 36
Let de = x, then DC = de + EC = x + 36
In RT △ AED, Tan ∠ DAE = Tan 30 ° = DEAE,
∴AE= 3x,∴BC=AE= 3x．
In RT △ DCB, Tan ∠ DBC = Tan 60 ° = dcbc,
∴ 3= x+363x,
∴3x=x+36,
x=18,
{DC = 54 (m)
（2）∵BC=AE= 3x,x=18,
The BC = 3 × 18 = 18 × 1.732 ≈ 31.18 (m)

What are the contributions of plants to human beings? There are five

1. Photosynthesis provides oxygen for human beings 2. It can purify the air 3. It provides all kinds of food for human beings 4. It provides shelter for human beings (now many rural houses still use wooden beams and windows) 5. The existence of plants maintains the balance of the ecosystem, which is the biggest contribution

Simplify 6A + 13A & nbsp; & nbsp; & nbsp; 6x-28-2.5x + 30.58a - (5a + 8) 5x + 7 - (4x + 0.18)

①6a+13a=19a②6x-28-2.5x+30.5=6x-2.5x+30.5-28=（6x-2.5x）+（30.5-28）=3.5x+2.5③8a-（5a+8）=8a-5a-8=3a-8④5x+7-（4x+0.18）=5x+7-4x-0.18=5x-4x+7-0.18=（5x-4x）+（7-0.18）=x+6.82

What is the general scale for drawing the school plan

Large display boards are generally 1 / 500, if drawn in the usual manual, it should be 1 / 1000 or less

Mathematician's story is less than 50 words

To sum up: the story of a mathematician -- Su Buqing was born in September 1902 in a mountain village in Pingyang County, Zhejiang Province. Although his family was poor, his parents saved money and worked hard for him to go to school