A problem of filling in the blanks in the first grade of junior high school The middle line on the waist of an isosceles triangle divides the triangle into two parts: 12cm and 21cm. Then the length of the bottom of the isosceles triangle is___________ . No picture!

Oh, shit. I just passed the exam
There are two cases
One is to take the first 12cm as the solution condition, then the number is 1.17cm
Second, if the second condition is 21cm, the number is 2.5cm
So the solution is 1.17cm or 2.5cm

If 2x = 43 and 3 (x + a) = a-5x have the same solution, then A-1 = 1___ ．

Solve the equation 2x = 43 to get: x = 23, substitute x = 23 into 3 (x + a) = a-5x to get the equation about a: - 6A = 16 to get: a = - 83, substitute a = - 83 into A-1 to get: A-1 = - 113

Is the power output of Xin'anjiang power plant transformed from heat energy or water energy

Hydroenergy

First question
A. B is 50 kilometers away from each other. A rides a motorcycle and B rides a bicycle from a to B. It is known that a's speed is 2.5 times that of B. B starts 1.5 hours earlier than a and arrives 1 hour later than a to find the speed of a and B
Second question
In order to adapt to the adjustment of agricultural structure, we are going to change part of the cultivated land to economic crops. After the change, the cultivated land for economic crops is 10% more than that for grain. How many hectares of cultivated land should be changed to economic crops?

1. Suppose that the speed of a is 2.5xkm/h and that of B is XKM / h
50/2.5x +1=(50-1.5x)/x
X = 12 --- B
V a = 12 * 2.5 = 30
2. It is suggested that x hectares of arable land should be converted to cash crops
x+150/400-x=11/10
10x+1500=4400-11x
21x=2900
x=138

How much is five liters of wine

The density of wine is about 0.8, and the quality of 5 liters of wine is 5 times 0.8, which is about 4 jin of wine

It is known that a2-6a + 9 and | B-1 | are opposite numbers, then the value of (AB − BA) / (a + b) is______ ．

From the meaning of the title, we know that a2-6a + 9 + | B-1 | = (A-3) 2 + | B-1 | = 0, | A-3 = 0, B-1 = 0, | a = 3, B = 1

When the resistance is zero, what is the relationship between voltage and current?

In theory, as long as there is a little voltage at both ends of the superconductor, the current will be infinite. But any power source has a certain internal resistance, and the current depends on the voltage and internal resistance of the power source, and its relationship still conforms to Ohm's law

A particle starts to move in a straight line from its rest. First, the acceleration A1 is used to make a uniformly accelerated linear motion, and then the acceleration A2 is used to make a uniformly decelerated linear motion until it stops. Given that the time of the whole process is t, the total distance of the object is

Suppose the total distance is s, the maximum speed is V (the final speed of the uniform acceleration stage is also the initial speed of the uniform deceleration stage), the time of the uniform acceleration stage is T1, and the moving distance is S1; the time of the uniform deceleration stage is T2, and the moving distance is S2, then in the uniform acceleration stage: S1 = A1 * T1 ^ 2 / 2 and V = A1 * T1 in the uniform deceleration stage

PEP junior high school physics concepts and all the formulas

1. Velocity: v = s / T 2, gravity: g = mg 3, density: ρ = m / V 4, pressure: P = f / S 5, liquid pressure: P = ρ GH 6, buoyancy: (1), f floating = f '- f (pressure difference) (2), f floating = G-F (apparent gravity) (3), f floating = g (floating, suspension) (4), Archimedes principle: F floating = g row =

As shown in the figure, a smooth metal ring with radius of R and mass of M is placed in the vertical plane, and a small ball with holes passes through the ring. At the same time, a string with length of R is tied to the ball at one end, and the other end is tied to the lowest point of the ring. When the ring rotates around the vertical diameter with angular velocity ω, the rope is straightened and the ball is subjected to two forces
A. 32gRB. 3gRC. gRD. 2gR

According to Newton's second law: F = mgcot30 ° = mrcos 30 ° ω 2, the solution is ω = 2gr. So D is correct, a, B and C are wrong. So D is selected

A problem of filling in the blanks in the first grade of junior high school The middle line on the waist of an isosceles triangle divides the triangle into two parts: 12cm and 21cm. Then the length of the bottom of the isosceles triangle is___________ . No picture!