Some problems on the representation of numbers by letters 1. Given x + y = 3, the value of 7-2x-2y is () 2.(M+N)-( ）=2M-P. 3. It is known that a is a two digit number with ten digit number x and one digit number y, and B is a two digit number with ten digit number y and one digit number x, then A-B = () (expressed by algebraic formula containing X and y)

Some problems on the representation of numbers by letters 1. Given x + y = 3, the value of 7-2x-2y is () 2.(M+N)-( ）=2M-P. 3. It is known that a is a two digit number with ten digit number x and one digit number y, and B is a two digit number with ten digit number y and one digit number x, then A-B = () (expressed by algebraic formula containing X and y)

1.7-2x-2y=7-2(x+y)=1
2.(m+n)-(-m+n+p)=2m-p
3.a-b=(10x+y)-(10y+x)=9x-9y

Examples of numbers represented by letters

AC + BC = (a + b) C multiplication combination law building number: block a, block B, block C sports ground, hall partition: A, B, C, D Poker: A, J, Q, K license plate number, such as Zhejiang a, a refers to Hangzhou poker, jqka scoring, a refers to advanced electronics: VCD, DVD, CCTV, CD and other dimensions: s ml x XL unit: kg, km, mm

What can numbers be represented by letters? What types can they be organized into? Please give examples
No less than 10, such as units, formulas, and examples

1. For example, s = vt
2. Calculation formula. V = sh
3. Operation law. A + B = B + A
4. Calculation method. A △ B = a × 1 / b
That's all. Letter units are not part of letter numbers

Take three examples of numbers represented by letters

A + B = B + a ask: what else? Answer: a × B = B × a, 2A = a × 2 add: a × B = B × a, 2A = a × 2

Use letters to represent the knowledge of numbers!
(15x Square) + (AX Square) + (x square) - 2
When a takes what value, the value of this algebraic expression is constant

Square of 15x) + (square of AX) + (square of x) - 2
=The square of (15 + A + 1) X-2
When 15 + A + 1 = 0, that is, when a = - 16, the value of this algebraic expression is constant - 2

The knowledge points of numbers expressed by letters in primary schools

Do mathematical formulas count?

All the knowledge points of numbers represented by letters
Please hurry up! The homework is urgent. I can't find my fourth grade math book. It's better to finish the problem in two hours!

Area s △ = bottom × height △ 2 = AXH / 2S rectangle = length × width = axbs parallelogram = bottom × height = axhs square = side length square = axas circle = π R2 (R is radius) s trapezoid = (upper bottom + lower bottom) × height △ 2 = (a + b) XH / 2 operation rule: a + B = B + a (a + b) + C = a + (B + C) a - (B + C) = a-b-ca - (B-C) = A-B

A question about numbers in letters
When a is an integer, the sum of polynomials a ^ 3-3a ^ 2 + 7a + 7 and 3-2a + 3A ^ 2-A ^ 3 must be ()
A. Multiple of 3
B. Multiple of 4
C. Multiple of 5
D. Multiple of 10

The sum of formula C 2 is 5 (a + 2), so it must be a multiple of 5

Use letters to represent a number problem
If the first polynomial is a ^ 2-2ab + 2B ^ 2, the second polynomial is 2 times less than the first polynomial by 3, and the third polynomial is the sum of the first two polynomials, find the sum of the three polynomials

The second polynomial is 2 * (a ^ 2-2ab + 2B ^ 2) - 3 = 2A ^ 2-4ab + 4B ^ 2-3
The third polynomial is a ^ 2-2ab + 2B ^ 2 + 2A ^ 2-4ab + 4B ^ 2-3 = 3A ^ 2-6ab + 6B ^ 2-3
The sum of the three polynomials is a ^ 2-2ab + 2B ^ 2 + 2A ^ 2-4ab + 4B ^ 2-3 + 3A ^ 2-6ab + 6B ^ 2-3 = 6A ^ 2-12ab + 12b ^ 2-6

As shown in the figure, square ABCD and square befg, point C is on side BG. It is known that the side length of square ABCD is a, and the side length of square befg is B. use a and B to represent the following areas. (1) area of △ CDE; (2) area of △ CDG; (3) area of △ CGE; (4) area of △ deg

(1) According to the meaning of the title, △ CDE area is 12a2; (2) according to the meaning of the title, △ CDG area is 12a (B-A) = 12ab-12a2; (3) according to the meaning of the title, △ CGE area is 12b (B-A) = 12b2-12ab; (4) according to the meaning of the title, △ DEG area = 12 (A2 + ab-a2 + B2 AB) = 12b2