Factorization 4 (a + b) ^ 2-16ab = - 4x ^ 2 (a-b) - 16y ^ 2 (B-A) And - 4x ^ 2 (a-b) - 16y ^ 2 (B-A)

Factorization 4 (a + b) ^ 2-16ab = - 4x ^ 2 (a-b) - 16y ^ 2 (B-A) And - 4x ^ 2 (a-b) - 16y ^ 2 (B-A)

4(a+b)^2-16ab=4(a²+2ab+b²)-16ab=4(a²-2ab+b²)=4(a-b)²
-4x^2（a-b）-16y^2(b-a) =-4(a-b)(x²-4y²)=-4(a-b)(x+2y)(x-2y)

It is known that the polynomial X & # 178; - 4xy + 3Y & # 178; + X + 11y + M can be decomposed into the product of two first-order factors, then the value of M is

We are going to let x \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\a + B = 1-3a-b = 11

The polynomial x ^ 2-4xy + M can be factorized into (x + 3Y) (x-7y), then the value of M is

(x + 3Y) (x-7y) expansion:
(x+3y)(x-7y)
=x^2-4xy-21y^2
Compared with the known polynomials, it is found that
m=-21y^2

Factorization of 3 times of X + 4 times of 4x-5-20x

3 times of X + 4 times of 4x - 5-20x
=(x^3-5)+4x(x^3-5)
=(x^3-5)*(4x+1)

The sequence {an} satisfies 3Sn = (n + 2) an (n belongs to n *), A1 = 2. (1) find the general term formula of the sequence {an}; (2) find the sum TN of the first n terms of the sequence {1 / an}
(hope to write the whole process Thank you...)

【1】 From the meaning of the title: 3Sn = (n + 2) an, it can be seen that: 3S (n + 1) = (n + 3) an, two formulas can be obtained by one subtraction, 3 * a (n + 1) = n * a (n + 1) + 3 * a (n + 1) - n * An-2 * an, that is, n * a (n + 1) = (2 + n) * an, that is, a (n + 1) / an = (n + 2) / N, thus an / a (n-1) = (n + 1) / (n-1). By this deduction, A3 / A2 = 4 / 2, A2 /

A square with a side length of 20 cm has the largest circle. The area of this circle accounts for 50% of the area of the square___ %．

3.14 × (20 △ 2) 2, = 3.14 × 100, = 314 (square centimeter); the square area is: 20 × 20 = 400 (square centimeter); so 314 △ 400 = 78.5%; answer: the area of this circle is 78.5% of the square area. So the answer is: 78.5

9 / 17 △ 7 + 8 / 7 × 1 / 17 (simple calculation)

1/7

Known samples x1, X2, X3 The variance of XN is 1, then the samples are 2x1 + 3, 2x2 + 3, 2x3 + 3 The variance of 2xn + 3 is ()
A. 1B. 2C. 3D. 4

Let x1, X2, X3 If the average of XN is m, then its variance is S12 = 1n [(x1-m) 2 + (x2-m) 2 + +(xn-m) 2] = 1, then sample 2x1 + 3, 2x2 + 3, 2x3 + 3 The mean of 2xn + 3 is 2m, and its variance is S22 = 4s12 = 4

There are two kinds of floor tiles in Xiaoming's living room and master bedroom. The living room covers an area of 36 square meters. Please choose a kind of floor tile. How much does it cost at least
30cm × 30cm 5 yuan / piece 50cm × 50cm 10 yuan / piece

6 * 6 = 36. Side length 600cm
50 * 12 = 600 cm. 12 * 12 = 144 pieces * 10 yuan / piece = 1440 yuan
30 * 20 = 600cm. 20 * 20 = 400 pieces * 5 yuan / piece = 2000 yuan
So it costs 1440 yuan to choose 50 * 50

If x > 0, then the minimum value of 4-x - (1 / x) is determined by the mean value theorem

There is no minimum value in this formula. For example, if x takes positive infinity, we will find that the formula is infinitesimal
4-x-(1/x)=4-(x+1/x)
X + 1 / x > = 2 (according to the mean value theorem)
So, 4-x - (1 / x)