Aunt Li bought 2 kg of apples and 2 kg of pears, which cost 20 yuan in total. It is known that 4.4 yuan per kg of pears, and how much is it per kg of apples Lie equation

Aunt Li bought 2 kg of apples and 2 kg of pears, which cost 20 yuan in total. It is known that 4.4 yuan per kg of pears, and how much is it per kg of apples Lie equation

Solution, set X yuan per kilogram of apples
2X+4.4x2=20
2X+8.8=20
2X=20-8.8
2X=11.2
X=11.2÷2
X=5.6

Uncle Zhang paid 36.8 yuan for 3 kg tomatoes and 2 kg cucumbers in the vegetable market. Aunt Li paid 35.2 yuan for 2 kg tomatoes and 3 kg cucumbers in the same vegetable market. How many yuan per kg tomatoes? How much is a kilogram of cucumber?

The price of 3kg tomato + 2kg cucumber = 36.8 yuan, the price of 2kg tomato + 3kg cucumber = 35.2 yuan, the price of 2kg tomato + 3kg cucumber = 32 yuan, the price of 5kg cucumber = 32 yuan

After class exercises of mathematics elective 4-4 in Senior High School
It is known that the center of the ellipse is o. major axis, the lengths of minor axis are 2a and 2B (a > b > 0), a and B are two points on the ellipse, and OA is vertical to ob
(1) It is proved that the sum of squares of the reciprocal of OA ob is a certain value
(2) Find the maximum and minimum area of triangle OAB. Thank you
Using polar coordinates. Thank you

Ideas: (1) the linear OA, OB equations and elliptic equations can be used to solve the univariate equation satisfied by the coordinates of points a and B, and then the square of the abscissa and ordinate of points a and B can be obtained and substituted into
1 | OA | 2 + 1 | ob | 2
(2) From s △ AOB = 12 | OA | ob |, 1 | OA | 2 + 1 | ob | 2 = A2 + b2a2b2, the minimum value can be obtained according to the mean inequality, and then according to s △ 2aob |=
14 | OA | 2 | ob | 2, transform | ob | 2 into | OA | 2, and then calculate the maximum area according to the | OA | range in the ellipse
(1) Let the elliptic equation be x2a2 + y2b2 = 1, let y = KX when the slope of OA exists and is not zero,
∵ a, B are two points on the ellipse respectively, and OA ⊥ ob. ‖ linear ob equation is y = - 1kx
Let a (x1, Y1), B (X2, Y2), and substitute y = KX into x2a2 + y2b2 = 1 to get X12 = a2b2b2 + a2k2, ∩ Y12 = k2a2b2 + a2k2
By substituting y = - 1kx into x2a2 + y2b2 = 1, we can get X22 = a2b2k2a2 + b2k2, ｜ Y22 = a2b2a2 + b2k2 1 | OA | 2 + 1 | ob | 2 = 1x12 + Y12 + 1x22 + Y22 = 1a2b2b2b2 + a2k2 + k2a2b2 + a2k2+
1a2b2k2a2+b2k2+a2b2a2+b2k2=a2+b2a2b2
When the slope of one of the lines OA and ob does not exist, then the slope of the other line is 0. At this time, 1 | OA | 2 + 1 | ob | 2 = 1A2 + 1b2 = A2 + b2a2b2
In conclusion, 1 | OA | 2 + 1 | ob | 2 is the fixed value
（2）S△AOB=12|OA||OB|,∴S△2AOB=14|OA|2|OB|2
According to (1), 1 | OA | 2 + 1 | ob | 2 = A2 + b2a2b2 ≥ 21 | OA | 21 | ob | 2 = 2 | OA | ob | 2|
∴S△AOB=12|OA||OB|≥a2b2a2+b2,∴S△AOBmin=a2b2a2+b2．
∵S△2AOB=14|OA|2|OB|2=14|OA|2(1a2+b2a2b2-1|OA|2)
=14 (1A2 + b2a2b2 | OA | 2-1 | OA | 4)
∵|OA|≤a,∴S△2AOB≤14(1a2+b2a2×b2×a2-1a4)=14a2b2
∴S△AOBmax=ab2
In conclusion, s △ aobmin = a2b2a2 + B2, s △ aobmax = AB2

The price of a commodity is 100 yuan. After 10% reduction, the price of the commodity will be reduced by 10%. The sales volume will soar. The shopping mall decides to increase the price by 20%. After the increase, the price of the commodity will be 10%
How much is it? Who will answer first

10% reduction: 100-100 * 0.1 = 90
Another 10:90-90 * 0.1 = 81
20% price increase: 81 + 81 * 0.2 = 97.2

A = the square of 1 + the square of 2 + the square of 3 +... + the square of 1999

Square of 1 + square of 2 + square of 3 + +The square of n = n (n + 1) (2n + 1) divided by 6. From this formula, we get a = 1999x2000x3999 / 6, so the bits of a are 0

Three equal area flower beds and three equal area lawns are 480 square meters in total. The flower beds are 10 square meters more than lawns

Area of each nursery:
(480-3 * 10) / (3 + 3) = 75 (M2)
Area of flower bed 75 + 10 = 85 (M2)
Setting: the area of each nursery is x, and the area of flower garden is x + 10
3X+3(X+10)=450
X = 75 (M2)
75 + 10 = 85 (M2)

1.3.7 × 0.8 means ()

3.7 × 0.8 means to divide 3.7 into 10 points averagely, of which 8 points is the number

What do you know about water and what do you know about saving water

Water is the source of life, the blood of industry and the lifeblood of the city. To cherish water is to cherish your life. Please cherish every drop of water. The world, China and cities are short of water. Please save water. Water is shameful and economical

We need 20 polyphonic words to serve the people

The first sound is a cut; the first sound is a cut; the third sound is a cut; the second sound is a cut; the second sound is a cut; the fourth sound is a cut; the second sound is a cut; the fourth sound is a cut; the fourth sound is a cut; the second sound is a cut; the fourth sound is a cut; the fourth sound is a cut; the fourth sound is a cut; the fourth sound is a cut; the fourth sound is a cut; the fourth sound is a cut

It is proved that in the parallelogram ABCD, AC & # 178; + BD & # 178; = 2 (AB & # 178; + BC & # 178;),
I'm an eighth grade student. AC & # 178; + BD & # 178; = 2 (AB & # 178; + BC & # 178;) don't use any cosine to prove that I haven't learned,

Let △ Abe ≌ △ DCF, let AE = DF = h, let AB = a, be = CF = x, EC = y, ｜ BC = x + y, BF = 2x + y, then AC & # 178; = H & # 178; + Y & # 178; BD & # 178; = H & # 178; be = CF = x, EC = y, BC = x + y, BF = 2x + y