If (a + b) &# 178; = m, (a-b) &# 178; = n, then a & # 178; + B & # 178; =, ab =

If (a + b) &# 178; = m, (a-b) &# 178; = n, then a & # 178; + B & # 178; =, ab =

That is a & # 178; + 2Ab + B & # 178; = M
a²-2ab+b²=n
Add
2a²+2b²=m+n
therefore
a²+b²=(m+n)/2
subtract
4ab=m-n
So AB = (m-n) / 4

The following expressions are equal to Mn ()
A. m+5n+5B. m−5n−5C. m2n2D. −m−n

A. If you add 5 to the numerator and denominator of a fraction at the same time, the value of the fraction will be changed and wrong; B. If you subtract 5 from the numerator and denominator of the fraction at the same time, the value of the fraction will be changed and wrong; C. if the numerator and denominator of the fraction are not multiplied by the same non-zero formula, the value of the fraction will be changed and wrong; D. according to the basic properties of the fraction, multiply the numerator and denominator of the fraction at the same time With - 1, the value of the fraction remains unchanged, which is correct

25a²-10a+1-b² (x²+9)²-36x²

25a²-10a+1-b²
=（5a-1）² -b²
=（5a-1+b）（5a-1-b）
(x²+9)²-36x²
=[(x²+9)+6x][(x²+9)-6x]
=（x+3）²（x-3）²

36x²-49=0(x

36x²=49
x²=49/36=(±7/6)²
x

How many square meters is 2 square kilometers? How many square meters is 1 hectare?

1 ha = 10000 M2
1 sq km = 100 ha
So: 2 square kilometers = 200 hectares = 2000000 square meters

The second power of (a + b) multiplied by the second power of (a-b) minus (a-b) (a + b) (the square of a + the square of B)

(a+b)²×(a-b)²–(a–b)(a+b)(a²+b²)=(a+b)(a–b)((a+b)(a–b)–(a²+b²))=(a²–b²)(a²–b²–(a²+b²))=–2b²(a²–b²)

Given the curve f (x) = x ^ 2 + 1 (1), find the tangent equation at point m (1,2) (2) find the tangent equation at point n (- 1,1)
Two questions are different

(1) The derivative of F (x) is 2x, so the slope of the tangent at M is 2 * 1 = 2, so the tangent equation is Y-2 = 2 (x-1), i.e. y = 2x (2). Let the intersection of the tangent passing through point n and f (x) be (a, a ^ 2 + 1) and the slope is 2A (a ^ 2 + 1-1) / (a + 1) = 2A. The solution is a = 0 or a = - 2. When a = 0, the slope is 0 and the tangent equation is Y-1 = 0 * (x + 1), i.e. y = 1

Simple calculation of 6.19 * 2.05 + 79.5 * 0.619
It has to be simple~

6.19*2.05+79.5*0.619
=6.19×2.05+7.95×6.19
=6.19×（2.05+7.95）
=6.19×10
=61.9

A number is 0.6 less than 75% of 12.8. What's the number?

12.8 × 75% - 0.6 = 9.6-0.6 = 9

The square of 3x + 6x = 0
Factorization method

The square of 3x + 6x = 0
3x（x+2）=0
X = 0 or x = - 2