Formula calculation: one fifth of a number is less than 80 percent of 30 by 7, find the number

(30 X 0.8-7) X 5= 85

Given that the square of (x + y) is 20 and the square of (x + y) is 40, find the sum of the squares of X + y and XY

(x+y)^2-(x-y)^2=40-20
x^2+2xy+y^2-(x^2-2xy+y^2)=20
x^2+2xy+y^2-x^2+2xy-y^2=20
2xy=20
xy=10
(x+y)^2=40
x^2+2xy+y^2=40
x^2+y^2=40-2xy=40-2×10=20

The square of (x-1) ^ 2-9 / 4 = 0 (x-1) minus 2 and 1 / 4 equals 0

(X-1)^2-9/4=0
(X-1)^2=9/4,
Square root on both sides:
X-1=±3/2,
X=1±3/2,
X1=1+3/2=5/2;
X2=1-3/2=-1/2.

If ABC is the three sides of a triangle
If a, B and C are the three sides of triangle ABC respectively, do we try to explain that the equation AX & # 178; + BX (x-1) = CX & # 178; - C must be a quadratic equation with one variable about x
By 6:30 a.m. on June 26, 2012, if no one answers, the best answer will not be adopted after this time

In a supermarket, the original price of a bag of milk is 2.4 yuan. The supermarket has a promotional activity of "buy two get one free". Granny Li wants to buy nine bags of milk. How much does it cost

"Find the maximum value of the function f (x, y) = e ^ - XY in the closed domain {(x, y) │ find the maximum value of the function f (x, y) = e ^ - XY in the closed domain {(x, y) │ x ^ 2 + 4Y ^ 2 ≤ 1}

Using Lagrange's theorem to calculate, the amount of calculation is large, and we hope to adopt it in time

In Xingxing fruit juice store, a kind of fruit juice is 1 yuan more expensive than B kind of fruit juice. Xiaobin and his classmates asked for 3 cups of B kind of fruit juice and 2 cups of a kind of fruit juice, which cost 16 yuan in total. What are the unit prices of a kind of fruit juice and B kind of fruit juice?

Suppose B juice is x yuan, then a juice is (x + 1) yuan. From the meaning of the question, 3x + 2 (x + 1) = 16, the solution is: x = 145, then a juice is 145 + 1 = 195 yuan. Answer: the unit price of a juice and B juice is 145 yuan and 195 yuan respectively

What is the result of simplifying the square of a in a + 2A?

Original formula = a (a + 2) / A
=a+2

On a map with a scale of 1:6000000, how many kilometers is the actual distance between a and B?
On a map with a scale of 1:6000000, the distance between a and B is 12 cm. What is the actual distance between a and B?

1: The scale of 6000000 indicates that the distance on the map is 1cm, which is equivalent to the actual distance of 60km
PS: 12 × 60 = 720km. The actual distance between a and B is 720km

1-2 + 3-4 +. + 2003-2004

1-2=-1,3-4=-1.2003-2004=-1
There are 1002 items, so it's equal to - 1002

Formula calculation: one fifth of a number is less than 80 percent of 30 by 7, find the number