Given x + y = 2, xy = - (1 / 2), find the value of X (x + y) &# 178; (1-y) - x (y + x) &# 178

Given x + y = 2, xy = - (1 / 2), find the value of X (x + y) &# 178; (1-y) - x (y + x) &# 178

x（x+y）²（1-y）-x（y+x）²
=x(x+y)²(1-y-1)
=-xy(x+y)²
=-（-1/2）×2²
=1/2×4
=2

If x (Y-1) - Y (x-1) = 4, then (X & # 178; + Y & # 178;) / 2-xy=

Solution
x(y-1)-y(x-1)=4
That is, xy-x-xy + y = 4
∴y-x=4
Two sides square
y²-2xy+x²=16
∴x²+y²=16+2xy
∴(x²+y²)/2-xy
=(16+2xy)/2-xy
=8+xy-xy
=8

If | X-2 | + X & # 178; - XY + 1 / 4 * y & # 178; = 0, find x, y

|x-2|+x²-xy+1/4*y²=0
|x-2|+(x-1/2y)²=0
x-2=0
x-1/2y=0
∴x=2
y=4

3 / 5 of a number is 7 / 8 of 30. What's the number
Determinant

Let this number be x, then there is
3/5*X=30*7/8
3/5X=105/4
X =105/4*5/3
x =175/4

How much do you weigh
There are two sentence patterns
How to use
A method of using what

How much do you weigh?
What's your weight?

Life tells me

To listen to life, to recall the trivial things in life, we will find that there are too many things in life worth remembering. There may be some life philosophy behind them. Life tells me that diligence can make up for clumsiness

How many kilowatts can 315 KVA transformer bring

Considering power factor 0.8, considering mechanical efficiency 0.9
So it should be: 315x0.8x0.9 = 226.8kw
If the heat dissipation can meet the requirement, 20% overload is allowed

If A-B = 3AB, find A-B + AB divided by 2a-2b + ab
Everyone help, online and so on

(a-b+ab)÷(2a-2b+ab)
=[(a-b)+ab]÷[2(a-b)+ab]
=(3ab+ab)÷(2×3ab+ab)
=(4ab)÷(7ab)
=4 out of 7

That is, q = I ^ 2 * r * t
Q=U*I*t
Q=U^2*t/R
Electric power P = UI
P=W/t
P=I^2*R
P=U^2/R
Which are applicable to all circuits, which are applicable to non pure resistance circuits and which are applicable to pure resistance circuits?
Please answer in detail, but not too difficult to understand,

Remember, electric power is based on current multiplied by voltage, which is applicable to all circuits; electrothermal is a Joule law, which is based on current square multiplied by resistance multiplied by time, which is applicable to all circuits

A person whose street lamp is 8m or 6m away from the ground walks at a speed of 84m / min. from the projection C of the street lamp on the ground, the change rate of the shadow length is calculated
It belongs to derivative problem

Let the shadow length be y and the time be X,
According to the similar triangle formula:
1.6/8=y/(y+84x)
The result is y = 21x
Derivation: y '= 21