Ask the master to help you solve it, and ask the big guy to help you solve it

(1) Let the tolerance of the equal difference series be d, then.

a3=a1+2d=10, s11=11a1+11 10 2d=11, the solution is a1=16, d=-3

The general formula for the series is: an=a1+(n-1)d=16-3(n-1)=19-3n

2) From (1) know an=19-3n, a1=16

Therefore sn=n(a1+an) 2=(19-3n+16)n 2=-3 2n 2+35 2n=-3 2(n-35 6) 2+1225 24

This parabolic opening is downward, and when n = 35 6, the sn is maximum. But because n is a positive integer, when n=5, sn=50;When n=6, sn=51>50

The maximum value of sn is 51, and n is 6

3. Solution: When the voltage source acts alone, the current source is open, as shown in the figure below

u'ab=10×6/（6+6）=5（v）。

When the current source acts alone, the voltage source is short-circuited, the left of the figure below, and the equivalent is redrawn to the right of the figure below

u"ab=2×6∥6=2×3=6（v）。

Superposition theorem: UAB=U'ab+u"ab=5+6=11（v）。

4. Solution: There are only two closed loops in the circuit: 2a i - 10v - 4.

So: i=2a, umb=6 i=6 2=12(v).

uam=10+4×3i=10+4×3×2=34（v）。

Therefore: uoc = uab = uam + umb = 12 + 34 = 46 (v).

Short-circuit the voltage source and open the current source. Apply voltage U to ports A and B, and set the incoming current to I. Obviously: i=i. Below:

According to KVL: U=4 (3I+I)+6 I=12I+4I+6I=22I.

So: req=u i=22( )

That is, the equivalent circuit parameters of Thevenin are: UOC=46V, REQ=22.

(1) Let the tolerance of the equal difference series be d, then.

a3=a1+2d=10, s11=11a1+11 10 2d=11, the solution is a1=16, d=-3

The general formula for the series is: an=a1+(n-1)d=16-3(n-1)=19-3n

2) From (1) an=19-3n, a1=16, so sn=n(a1+an) 2 =(19-3n+16)n 2=-3 2n 2+35 2n=-3 2(n-35 6) 2+1225 24

This parabolic opening is downward, and when n = 35 6, the sn is maximum. But because n is a positive integer, when n=5, sn=50;When n=6, sn=51>50

The maximum value of sn is 51, and n is 6

A, 6 (two) + 10 (two) = 1 catty.

One pound in Taiwan is now equal to 16 taels, the same as in old China. The old weights and measures in ancient China also used the 16 taels system.

b. 6 (ounces) + 10 (ounces) = 1 pound;

c. 6 (weeks) + 10 (weeks) = 1 (quarter); 16 weeks = 4 months, April is the first quarter.