It is known that four real numbers - 9, A1, A2 and - 1 are equal difference sequences, and five real numbers - 9, B1, B2, B3 and - 1 are equal proportion sequences, then B2 (a2-a1) = () A. 8B. -8C. ±8D. 98

It is known that four real numbers - 9, A1, A2 and - 1 are equal difference sequences, and five real numbers - 9, B1, B2, B3 and - 1 are equal proportion sequences, then B2 (a2-a1) = () A. 8B. -8C. ±8D. 98

From the question, we get a & nbsp; 2 − A & nbsp; 1 = D = − 1 + 94 − 1 = 83, B22 = 9, and because B2 is the third term in the equal ratio sequence, it has the same sign with the first term, that is, B2 = - 3  B2 (a2-a1) = - 8

In the triangle ABC, a = 2bcosc, then what is the triangle?

It's an isosceles triangle, and a is the vertex
Well, it's very simple
Combined with sine theorem, a / b = Sina / SINB
Then a = 2bcosc
It is reduced to Sina = 2sinbcosc
And ∵ Sina = sin (π - B-C) = sin (B + C) = sinbcosc + sinccosb
∴sinBcosC+sinCcosB=2sinBcosC
∴sinBcosC=sinCcosB
∴sinBcosC-sinCcosB=0
That is sin (B-C) = 0
The range of B-C in a triangle is (- π, π)
∴B-C=0
∴B=C
The triangle is an isosceles triangle with vertex a, ab = AC

In the triangle ABC, the opposite sides of the angle ABC are ABC and satisfy a = 2bcosc
If the area is root 3, B + C = 4, find a

It is proved that (1) ∵ a = 2bcosc ∵ a = 2B * (a ^ 2 + B ^ 2-C ^ 2) / 2Ab ∵ a ^ 2 = a ^ 2 + B ^ 2-C ^ 2 ∵ B ^ 2 = C ^ 2, that is, B = C (2) ∵ B + C = 4, B = C ∵ B = C = 2, s = b * c * Sina / 2 = radical 3 ∵ Sina = (radical 3) / 2, then a = 60 ° ∵ B = C ∵ triangle ABC is equal

In resistance circuit, voltage and current () in pure inductance circuit, voltage () current () in pure capacitance circuit, current () voltage ()

The resistance is the same, the inductance is different, the capacitance is different

A light spring with stiffness coefficient K is used to tie a wood block with mass m on a smooth horizontal plane
On a smooth horizontal plane, a light spring with stiffness coefficient K is used to tie a wood block with mass m, and a horizontal external force F is used to push the wood block to compress the spring, which is in a static state. When the external force F is suddenly removed, the speed of the block is_ And the acceleration is_ In the initial stage, the wood block was used for making_ motion

0, 0, uniform linear motion

The relationship between the area y and the length x of the hypotenuse of a right triangle ABC with an angle of 60 '
RT

A right triangle ABC with an angle of 60 'and a hypotenuse length of X
The length of the shorter right angle is x / 2
Height on bevel
=(x/2)*sin60'
=(√3)x/4
therefore
y=x*[(√3)x/4]/2
y=(√3)x²/8

A light spring can be extended by 8 mm with a force of 5 n. now it is pulled by a force of 10 N at both ends. At this time, the extension of the spring should be ()
A. 4mmB. 8mmC. 16mmD. 32mm

Let the spring stiffness coefficient be K, when the spring is pulled with 5N force, F1 = kx1; when the spring is pulled with 10N force, F2 = kx2; the simultaneous solution is x2 = f2f1x1 = 105 × 8mm = 16mm; therefore, C

A mixed operation of rational numbers is required to include five kinds of operations: addition, subtraction, multiplication and division. The divisor is a negative fractional power, and the base is a fractional power. The result is equal to 2009
Please use words to express, because some symbols can't be understood

(1 and 1 / 2 power) plus (3 / 4) minus [(- 2 / 3) divided by (2 / 3) multiplied by (2006)] = 2009
Brackets are just for the convenience of reading. When you write the formula, you can do without them. Is this OK
Don't understand, please accept, I wish you a happy study!

As shown in the figure, the pulley block increases the weight of 100N object by 0.5m, and the work done by pulling force is 60j. 1. The mechanical efficiency of pulley block 2. The pulling force at the free end of rope
(3) If the weight of moving pulley is known to be 18N, how much work can be done to overcome friction in this process

The mechanical efficiency of pulley block is η = GH / W, total = 100N × 0.5m △ 60j = 5 / 6 ≈ 83.3%. 2. The tension at the free end of the rope is: ∵ wtotal = FS = FNH, that is, 60j = f × 4 × 0.5m, ∵ f = 30n3

In the sequence {an}, an = 32, Sn = 63, (1) if the sequence {an} is an arithmetic sequence with tolerance of 11, find A1; (2) if the sequence {an} is an arithmetic sequence with A1 = 1 as the first term, find the first m term and SM ′ of the sequence {AM2}

(1) ∵ n (a1 + an) & nbsp; 2 = Sn = 63, a1 + (n-1) 11 = an = 32, the solution is A1 = 10. (2) A1 × QN − 1 = 32, A1 (1 − QN) 1 − q = 63, the solution is q = 2, n = 6 ℅ so {an2} is an equal ratio sequence with the first term of 1 and the common ratio of 4, SM = 1 × (1 − 4N) 1 − 4 = 4N − 13