How to solve the equation of (130-x) / (70 + x) = 4 / 1?

How to solve the equation of (130-x) / (70 + x) = 4 / 1?

(130-x)\(70+x)=4
130-x=280+4x
130=280+5x
150=5x
x=30

(x-3) × 1.8 = 7.2 help me solve this equation,

（x-3）x1.8=7.2
x-3 =7.2/1.8
x-3 =4
x=4+3
x=7

((x-1) / x) - 1 / x = 7 / 8 solve the equation

((X-1)/X)- 1/X =7/8
1-1/x-1/x=7/8
1/8=2/x
x=16

Mathematical problems 125 × 0.1999 + 2 × 1.25 × 19.99 + 1250 × 0.01999

125×0.1999+2×1.25×19.99+1250×0.01999
=125×0.1999+2×1.25×19.99+1250×0.01999
=1.25X19.99+2X1.25X19.99+1.25X19.99
=19.99X(1.25+2X1.25+1.25)
=19.99X5
=20X5-0.01X5
=100-0.05
=99.5

Let a be an idempotent matrix, it is proved that a + E and e-2a are invertible matrices and their inverses are obtained

If a ^ 2-A = 0, do a division with remainder, a ^ 2 + a-2a-2e = (a + e) (a-2e) = - 2E, so the inverse matrix is obvious
Another method is to deduce that the eigenvalue of a can only be 0 or 1 from a ^ 2-A = 0, then the eigenvalue of a + e is non-zero, so it is reversible. However, if we use this method to solve the inverse, we need to verify that a can be diagonalized, which is relatively troublesome

A two digit number, one digit number is 5 larger than ten digit number. If the positions of the two digits are exchanged, then the sum of the new number and the original number is 143. Find the two digit number

Let the tens of bits be x, and the bits be x + 5. The original number is 10x + X + 5. After the exchange, it is 10 × (x + 5) + X, that is, 10x + X + 5 + 10x + 50 + x = 143

Calculation. Given that the eigenvalues of 3-order square matrix A are 1,2, - 3, find the value of determinant | a ^ - 1 + 3A + 2e |

g(x) = 1/x +3x +2
Because the eigenvalues of a are 1,2, - 3
So the eigenvalues of G (a) = a ^ - 1 + 3A + 2E are g (1) = 6, G (2) = 17 / 2, G (- 3) = - 22 / 3
So | a ^ - 1 + 3A + 2e | = 6 * (17 / 2) * (- 22 / 3) = - 374

What is the formula of the equation of the vertical bisector of a line? How to find it?

Let a (x1, Y1) B (X2, Y2), then the coordinate of the midpoint C is {(x1 + x2) / 2, (Y1 + Y2) / 2}. From the slope of AB k = (y2-y1) / (x2-x1), we can get the slope of the vertical bisector l of AB: - 1 / K

The value range of number a in scientific notation
Brothers and sisters, please do me a favor. It's urgent

A belongs to (0,10)

Xiao Ming read 20% of the whole book on the first day, 25% more on the second day than on the first day, and 12 pages on the third day,
I've just read half of this book. How many pages is it? Please,

（1+0.25）*0.2=0.25 0.5- 0.25-0.2=0.05 12/0.05=600