Binary linear equation application problem If x toys are produced every day, the cost of toys is r = 20x + 600, the selling price is p = 200-2x, and the profit is 3400 yuan. How much is x? Find the equation, find out how to solve this equation! I know how to make equations, but I still can't solve them. How do you solve them?

Binary linear equation application problem If x toys are produced every day, the cost of toys is r = 20x + 600, the selling price is p = 200-2x, and the profit is 3400 yuan. How much is x? Find the equation, find out how to solve this equation! I know how to make equations, but I still can't solve them. How do you solve them?

The meaning of the question is: produce x per day
X(200-2X) -(20X+600）=3400
200X-2x²-20X-600=3400
180X-2x²-4000=0
2x²-180x+4000=0
x²-90x+2000=0
(X-40)(X-50)=0
Ψ x = 40 or x = 50
Ψ X1 = 40, X2 = 50 (50 > 48, rounding off)
Answer: should produce 40 toys every day, can make profit 3400 yuan

Application of quadratic equation in Grade 9 of junior high school
In a meeting, every two people shake hands once. According to statistics, they shake hands 66 times. How many people attended the meeting?

A total of 12 people attended the meeting
The equation is x * (x-1) / 2 = 66
The solution is x = - 11 or 12, - 11 No, take 12

Junior high school grade one volume two binary linear equation application problem
It is known that the solution of the equations of X, y in braces (upper) 2x + 3Y = K (lower) 3x-4y = K + 11 satisfies the equation 5x-y = 3, and the value of K is obtained

2X+3Y=K,3X-4Y=k+11
Add
2X+3Y+3X-4Y=K+K+11
5X-Y=2K+11
5X-Y=3
So 2K + 11 = 3
K=-4

One to problem: 0.75 * 3.16 + 7.84 * 75% - 75% solution: 3x-120% x = 0.45

0.75*3.16+7.84*75%—75%
=0.75*3.16+7.84*0.75-0.75
=0.75*（3.16+7.84-1）
=0.75*10
=7.5
3x—120%x=0.45
3x-1.2x=0.45
（3-1.2）x=0.45
1.8x=0.45
x=0.25

How to calculate the edge length of a cube

There is no circumference in a cube. If the sum of edges is known, divide it by 12. If the surface area is known, divide it by 6

If cos (a - π / 6) = 12 / 13 and π / 6 < a < π / 2, then cosa =

∵π/6

To solve the equation, 1 / 4 x + 3 / 4 x = 3 [2 / 5 + 1 / 2] x = 5 / 3 x * 10 / 9 * 5 / 18 = 100 / 9
[2 / 5 + 1 / 2] x = 5 / 3, the second is x * 10 / 9 * 5 / 18 = 100 / 9

(1 / 4) x + (3 / 4) x = 3, the answer is x = 3

Given that one root of the equation x2 + mx-6 = 0 about X is 2, then the other root of the equation is 2______ ．

∵ one root of the equation x2 + mx-6 = 0 is 2, let the other be a, ∵ 2A = - 6, the solution is a = - 3, then the other root of the equation is - 3. So the answer is: - 3

If the focus of the ellipse x ^ 2 / A ^ 2 + y ^ 2 / b ^ 2 = 1 is on the X axis, make the tangent of the circle x ^ 2 + y ^ 2 = 1 through the point (1.1 / 2)
If the tangent points are a and B, and the line AB just passes through the right focus and upper vertex of the ellipse, what is the elliptic equation?

Let point (1,1 / 2) be p, then it is easy to prove: Po ⊥ ab
The slope of Po = (1 / 2-0) / (1-0) = 1 / 2, and the slope of AB = - 2
From the coordinates (1,1 / 2) of point P and the equation of circle: x ^ 2 + y ^ 2 = 1, it is obtained that:
A. One of B is the intersection of the circle and X axis, and the coordinates of this intersection are (1,0) and (1,0)
The equation of AB is y = - 2 (x-1), that is, y = - 2x + 2
∵ the focus of the ellipse x ^ 2 / A ^ 2 + y ^ 2 / b ^ 2 = 1 is on the X axis, and the upper vertex coordinates of the ellipse are (0, b)
∵ the line AB passes through the upper vertex of the ellipse, ∵ (0, b) satisfies the equation of the line AB, B = 2, ∵ B ^ 2 = 4
Easy to get: the right focus coordinate of the ellipse is (√ (a ^ 2-B ^ 2), 0), and the line AB passes through the point,
∴0＝－2√（a^2－b^2）＋2＝0,∴a^2－b^2＝1,∴a^2＝1＋4＝5.
Therefore, the elliptic equation satisfying the condition is: x ^ 2 / 5 + y ^ 2 / 4 = 1

A simple method is used to calculate the following questions: (1) - 2 of 13 × 3-0.34 × 2 of 7 + 1 of 3 × (- 13) - 5 × 0.34 of 7
(2) (+ 33 1 / 3) × (- 2.5) × (- 7) × (+ 4) × (- 0.3)

1. - 2 / 13 × 3-0.34 × 2 / 7 + 1 / 3 × (- 13) - 5 / 7 × 0.34
=- 13 × (2 / 3 + 1 / 3) - 0.34 × (5 / 7 + 2 / 7)
=-13-0.34
=-13.34
2. (+ 33 1 / 3) × (- 2.5) × (- 7) × (+ 4) × (- 0.3)
=33 and 1 / 3 × 70 × (- 0.3)
=33 and 1 / 3 × - 21
=-700