How to use cross multiplication calculation

How to use cross multiplication calculation

The method of cross multiplication is simple: multiplication on the left side of the cross equals the coefficient of the quadratic term, multiplication on the right side equals the constant term, cross multiplication and addition equals the coefficient of the primary term
Cross multiplication can factorize some quadratic trinomials

Let y = (x ^ 2), find dy / DX
Let y = sinu, u = x ^ 2, then
Why is dy / Du multiplied by Du / DX = sinu / u multiplied by x ^ 2 / X equal to COSU multiplied by 2x

I don't know if your problem is related to the formula in the following content, but the derivative of sinu is equal to COSU, and the derivative of x ^ 2 is equal to 2x. You can study it yourself or write down the content of the problem. I'm helping you study it

Is the density of aluminum 2.7g/cm3 or 2.7g/cm3?

2.7 grams per cubic centimeter or 2.7 * 10 cubic kilogram per cubic meter

Factorization, cross multiplication
Factorization a ^ 2-B ^ 2-6a-4b + 5
Cross multiplication: 10x ^ 2-xy-2y ^ 2

a^2-b^2-6a-4b+5
=(a-3)^2-(b+2)^2
=(a+b-1)(a-b-5)
10x^2-xy-2y^2
=(2x-y)(5x+2y )

How to prove: X radical 2 + y radical 2 + Z radical 2 = a radical 2 (a > 0), the intercept of tangent plane of any point on each coordinate axis is a
incorrect,
How to prove that: X radical 2 + y radical 2 + Z radical 2 = a radical 2 (a > 0), the sum of the intercept of the tangent plane of any point on each coordinate axis is a
We need to work out the tangent plane first

If the intercept is not a, then
1 in X plane, y = 0, z = 0, then x radical 2 = a radical 2 equation in X plane intercept is a
2 in Y plane, x = 0, z = 0, then y radical 2 = a radical 2 equation in Y plane intercept is a
3 in z plane, x = 0, y = 0, then Z radical 2 = a radical 2 equation in z plane intercept is a
Contrary to the hypothesis, so the hypothesis does not exist, so the proposition is true!

Is 80 miles 80 kilometers per hour?

Mathematics alone is not correct
But when Chinese people talk about driving speed, they are used to taking miles

Fill in the brackets with the unit 1 () - 1 () = 999 () 1 () - 1 () = 23 () 1 () - 1 () = 59

10 (ten million) - 10 (ten thousand) = 9.99 (ten thousand)
1 (day) - 1 (hour) = 23 (hour)
1 (hour) - 1 (minute) = 59 (clock)

If the vertex of the minor axis and two focal points of the ellipse form an equilateral triangle, the ratio of the focal length to the length of the major axis is 0

Suppose the focus is on the X axis
F1(-c,0),F2(c,0)
B(0,b)
Bf1f2 is an equilateral triangle
According to the plane geometry, Bo / F1F2 = √ 3 / 2
That is, B / 2C = √ 3 / 2
b/c=√3
b^2=3c^2
a^2=b^2+c^2=4c^2
So C / a = 1 / 2
2c/2a=1/2
So the ratio of focal length to long axis length is 1:2

One side of a rectangle is 5A + 3b, and the other side is A-B smaller than it

If x and y satisfy the equation 2x − 3Y = − 54x + 9y = − 7, then x + y=______ ．

2x − 3Y = − 5, ① 4x + 9y = − 7, ②, ① + ② get: 6x + 6y = - 12, then x + y = - 2