-3x m-2n * y m+n+ 1/5 * x 5 * y 6 has four terms, and the unknowns are x, y, xy and a constant term, so these cannot be combined, so only the sum of the terms containing m and n is required to be 0, that is, -3x m.
At this time, (m-2n) 2-5 * (m+n)-2 * (m-2n) 2+m+n = 6? + 15-2×6? +0-3=-24
2. because it has nothing to do with x, it does not contain X.
In -3x 2+MX+NX 2-x+3, when n=3 and m= 1, the x term is not included.
3. Similar terms mean that they contain the same letters and have the same number of times, regardless of the coefficient, so
3x 4 * y, with letter x, degree 4, with letter y, degree 1. -1/3x m * y n, with the letter x, the degree is m, with the letter y, the degree is n, according to the definition, m=4, n= 1.
4.a, (x+ 1) 2, x+ 1 may be equal to 0, because the value of x is uncertain, so it is not necessarily a positive number. The value of b, x+ 1| may also be 0. ? C, (-x) 2+ 1, because (-x) 2? ≥0, so adding 1 must be greater than 0. D, -x 2+ 1, only -x 2 >- 1 is a positive number.
5. Because x-y=2, y-x=-2 is brought into the formula (X-Y) 2+2 (Y-X)+5 = 2? +2×(-2)+5=5
6. If the number A is X and the sum of the numbers A and B is 5, then the number B is 5-x, and their product is x(5-x)=5x-x?
7.y/m means 1 kg of rice.
8. The number with the smallest absolute value is 0, the square number is 0, 1, the cubic number is-1, 0, 1, and the reciprocal is-1.
9. If the distance is S, then s/x is the speed of A and s/y is the speed of B. To simplify, the meeting time =s/(s/x+s/y), and the available time is XY/X+Y.
10 、( b+ c)-(a-d)= b+ c-a+d = b-a+c+d =-(a-b)+(c+d)= 3+2 = 5
1 1, the question is a formula (minuend)-? Another formula (subtraction)? =? The formula (difference) on the right, so you can subtract the difference on the right from the one on the left and find the one in brackets. (3a 2-2ab-B2)-(-5a 2+a b-2b 2)= open = 8a？ -3ab+b？ .
12, ① X 2+XY = 2, Y 2+XY = 7, so X 2+Y 2 = 2+7-XY = 9-2XY.
② A 2-AB = 3, B 2+AB = 2, so A 2+B 2 = 3+AB, then A 2+B 2 = 3+AB+2-AB = 5.
13, ① in sequence, the common ratio is-3, so the fourth item =45×-3=- 135.
(2) this question is to look at the known and find the law.
A2=a 1*q, and A2 corresponds to 1 power 2- 1 of q.
a3=a 1*q^2？ A3 corresponds to the quadratic power 3- 1 of q.
a4=a 1*q^3？ A4 corresponds to the third power of Q 4-1.
…… ?
an=a 1*q^(n- 1)？ n- 1
(3) The second term is 10, the third term is 20, and the common ratio is 2, so the first term is 10/2=5 and the fourth term is 20*2=40.
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