If x (Y-1) - Y (x-1) = 4, find the value of x2 + Y22 − XY

If x (Y-1) - Y (x-1) = 4, find the value of x2 + Y22 − XY

∵x（y-1）-y（x-1）=4，∴xy-x-xy+y=4，∴y-x=4，∴x-y=-4，∴x2+y22−xy=(x−y)22=(−4)22=8．

2. If y = 3x (XY is not equal to 0), then XY is proportional to ()? 1. If x = 7 / y, XY is proportional to ()?

2. If y = 3x (XY is not equal to 0), then XY is (positive) proportional
1. If x = 7 / y, XY is (inversely) proportional

What's the physical symbol of delta T

Physically, it means temperature difference

If the obstinacy coefficients of the two springs are different, can the periodic formula of the vibration system be derived? How can it be verified by experiments?

Yes. First in series, measure the overall stiffness coefficient as a spring; then in parallel, measure the same
The former K is similar to the formula of resistance in parallel for R, while the latter is similar to resistance in series

The rated power of "pz220-100" bulb connected to 110V circuit is____ What is the actual power____ .
Please give the detailed process

100W
25W
P = u squared / R
R is fixed
If the voltage is reduced by half, the power will be reduced by four times

The stiffness coefficient of a light spring is k = 500N / m. pull the spring with 100N force at both ends of the spring along the opposite direction of the axis, and the spring will be extended______ ．

According to the meaning of the question, the elastic force of the spring is f = 100N, and the stiffness coefficient is k = 500N / m. according to Hooke's law f = KX, x = FK = 100n500n / M = 0.2m, so the answer is: 0.2m

An isosceles right triangle, only know hypotenuse length 10, how to find area?

Hypotenuse 10 is an isosceles right triangle, so its height is 5, so it is 5 × 10 / 2 = 25

75% of 20kg is what percentage of 30kg

20×75％=15
15÷30×100％=50％

6, 8, 9, 9 these four numbers. How to use addition, subtraction, multiplication and division to 18

8×9-6×9=2×9=18

An object is pulled by 90N in the vertical direction and moves upward at a uniform speed of 0.2m/s. (air resistance is not included) (1) (2) the gravity of the object. (3) as shown in the figure, if the pulley block with mechanical efficiency of 80% is used, the object can still move to the right at a speed of 0.2m/s with a tensile force of 10N, and the useful power of the object can be calculated within 10s

(1) ∵ v = st, ∵ the rising distance of the object: S = VT = 0.2m/s × 10s = 2m; (2) the object moves vertically in a straight line at a constant speed and is in a state of equilibrium. According to the equilibrium conditions, g = f = 90N; (3) the distance of the object: S = VT = 0.2m/s × 10s = 2m; according to the pulley block shown in the figure, n = 3, the rope is from