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If A2 + B2 + c2-ab-3b-2c + 4 = 0, then the value of a + B + C is______ ．
A2 + B2 + c2-ab-3b-2c + 4 = 0a2-ab + 14b2 + 34 (b2-4b + 4) + c2-2c + 1 = 0 (a-12b) 2 + 34 (b-2) 2 + (C-1) 2 = 0 〈 a-12b = 0, 34 (b-2) = 0, C-1 = 0 〈 a = 1, B = 2, C = 1, then a + B + C = 4
The first step is to find the value of the algebraic formula X / X-2 △ (2 + x-4 / 2-x), where x = 2sin45 ° - 1
Fill in the blanks: if a store sells a color TV at a 10% discount, it will make a profit of 20%. If the purchase price of the color TV is 2400 yuan, what is the price of the color TV
Second, set the price of color TV to X
Then x * 90% = 2400 * 1.2
The solution is x = 3200
As shown in the figure, in the known trapezoid ABCD, ad ‖ BC, ∠ B = 90 °, ad = 3, BC = 5, ab = 1, rotate the line CD 90 ° counterclockwise around point d to the de position, and connect AE, then the length of AE is___ ．
As shown in the figure, make ef ⊥ ad in F, DG ⊥ BC in G. according to the nature of rotation, de = DC, de ⊥ DC, ∠ CDG = ∠ EDF, ≌ CDG ≌ EDF, DF = DG = 1, EF = GC = 2, ≌ AE = 16 + 4 = 25
When a ship sails between a and B, it is known that the distance between a and B is s km. From a to B, it is downstream, from B to a, it is upstream. The speed of the ship in still water is a km / h, and the water speed is B km / h (a > b). The average speed of a round trip between a and B is calculated
A to B is downstream, time T1 = s / (a + b)
From B to a is the reverse water, time T2 = s / (a-b)
Average velocity = 2S / (T1 + T2) = 2S / [S / (a + b) + S / (a-b)] = (a ^ 2-B ^ 2) / A
The area of a circle and a square is 2 π cm2. Which of them has a larger perimeter? What can you learn from it?
(1) Let the radius of the circle be RCM, then π R2 = 2 π, the solution is r = 2, then the circumference of the circle is 2 π r = 2 π × 2 ≈ 8.88; let the side length of the square be ACM, then A2 = 2 π a = 2 π≈ 2.506, then the circumference of the square is 4A ≈ 10.02 ＞ 8.88, then the circumference of the square is larger. (2) enlightenment: when the surface product of the circle and the square is equal, the circumference of the square is larger
How to calculate 7 out of 12 + 2 + 5 out of 12
Add fractions first and then integers
Y = lgx + logx (10) and (x > 1)
Process,, (x is the base, 10 is the index)
Using the formula loga (b) = logC (b) / logC (a)
Then y = lgx + logx (10)
=lgx+lg10/(lgx)
=lg x + 1/lg x
Because x > 1, lgx > 0
From the mean inequality, LG x + 1 / LG x ≥ 2 √ (lgx) (1 / lgx) = 2
If and only if lgx = 1 / lgx, the minimum value 2 is obtained, that is, if x = 10, the minimum value 2 is obtained
So the range is [2, + ∞]
The side length of a square is 4cm, the perimeter and area are equal ()
Judgment questions
The side length of a square is 4cm, the perimeter and area are equal ()
9 kilograms of iron is as heavy as 9000 grams of cotton ()
From 7:00 to 9:15, 115 points ()
A second hand on a clock is a minute
The length of the ridge is 6cm. The cube has the same surface area and volume ()
The volume unit ()
Fill in the blanks
There are () big months () small months in a year, and () days in the first quarter of a normal year
1900 is () year, with () days in the whole year and () days in February
Master Chen arrives at school at 8:00 in the morning and leaves work at 16:00 in the afternoon. His working hours are () hours in total
The teacher's Day party starts at 15:30 and ends in 3 hours and 50 minutes, ending at () hours and () minutes
With the edge length of 1 cm small cube can be divided into () cubic decimeter small cube
At least 1 cm cube with () edges can form a large cube
From 7:00 to 9:15 after 115 minutes (wrong) on the clock, a second hand walk is one minute (right) edge length 6 cm cube, surface area and volume equal (wrong) record wall
4.4.10.10. How is it equal to twenty-four
√4＋√4＋10＋10＝24
Given the sequence (an), A1 = 2, 6sn = (an + 1) (an + 2), find the general term formula (an) and the first n term and Sn of the sequence (an)
6Sn=(an+1)(an+2)=an^2+3an+2
6S(n+1)=a(n+1)^2+3a(n+1)+2
Subtraction of two formulas
6a(n+1)=a(n+1)^2-an^2+3a(n+1)-3an
a(n+1)^2-an^2-3a(n+1)-3an=0
a(n+1)^2-an^2=3a(n+1)+3an
[a(n+1)+an][a(n+1)-an]=3[a(n+1)+an]
So a (n + 1) = - an or a (n + 1) = an + 3
①a(n+1)=-an
an=2*(-1)^(n+1)
Sn=1+(-1)^(n+1)
This sequence is 2, - 2,2, - 2 So the odd term is 2 and the even term is - 2
And (- 1) ^ (n + 1), when n is odd, that is, N + 1 is even, (- 1) ^, even = 1
When n is even, that is, N + 1 is odd, (- 1) ^ odd = - 1, then multiply the formula by 2 to express the sequence
And Sn is 2,0,2,0 In this way, the odd term is 2 and the even term is 0
This can be understood as odd = 1 + 1, even = 1 + (- 1)
So we can also use (- 1) ^ (n + 1) plus 1 to express SN
②a(n+1)=an+3
This is a very simple arithmetic sequence
The first item is 2 and the tolerance is 3
So an = a1 + (n-1) d = 2 + 3 (n-1) = 3n-1
Sn=n(a1+an)/2=n(2+3n-1)/2=(3n^2+n)/2=3/2n^2+n/2
PS: roar, don't think that a (n + 1) + an = 0 must be abandoned. In fact, it's OK. It completely meets the requirements of the title
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