In the difference series an, if a3 a4 a5 a6 a7 450, then S9 ?

a1 + a2 + a8 + a9 = = a3 + a4 + a6 + a7 = 4a5 so 5 a5 = 450 to get a5 = 90

So s9 = a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 = (a1 + a2 + a8 + a9) + (a3 + a4 + a6 + a7) + a5 = 9 a5 = 810

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Answer]: C according to the nature of the difference series: a3 + a7 = a4 + a6 = 2a5, so brother pants state a5 = 90, so a2 + a8 = 2a5 = 180 should choose (c).

Instructions] This question mainly examines the candidate's solution to the definition of the equal difference series, the formula of the common term of the source and the properties of the equal difference series If it is an equal pure family difference series, and m+n=k+l (where m, n, k, l are all positive integers), then there is am+an=ak+al Applying this property in the solution can simplify the operation If this problem is directly solved by applying the general formula of the equal difference series and the first n terms and formulas, the operation is more complicated

Arithmetic progression. a4+a6=2a5=80

So a5=40

s5=a1+a2+a3+a4+a5=5a3=10, so a3=2

Solution: According to the nature of the term in the difference.

a3+a7=2a5

a4+a6=2a5

So a3 + a4 + a5 + a6 + a7

a3+a7)+(a4+a6)+a55a5

Get a5=90

So A2 + A8 = 2A5 = 2 90 = 180 choose C

Select c and set the tolerance to d, the original formula is equal to 5(a3+a7) 2=450, since a7=a3+4d, so a3+2d=90

a2+a8=a3-d+a3+5d=2a3+4d=180

Let me tell you a formula: if m+n=2q, then in the proportional series, there is an+am=2aq

So, the complete process of your topic is:

Solution: (a3+a7)+(a4+a6)+a5=2a5+2a5+a5=450

a5=90a2+a8=2a5

a2+a8=180

Solution: I think that an is a series of equal differences, so a2+a8=a3+a7=a4+a6=2a5, and because a3+a4+a5+a6+a7=50, so 2*(a2+a8)+, the solution is a2+a8=50

The key is to grasp that this is a series of equal differences, the first term + the last term = the second term + the penultimate term.

a3+a4+a5+a6+a7=450 and is a series of equal differences, so 5a5=450

So a5=90

So a2+a8=2a5=2*90=180

This question was changed by mistake.

In the series of equal differences, if a3 + a4 + a5 + a6 + a7 = 450Beg.

a2+a8.

a3+a4+a5+a6+a7=450

An is a series of equal differences.

a5=90a2+a8=2a5=2*90=180

a1 + a2 + a8 + a9 = = a3 + a4 + a6 + a7 = 4a5 so 5 a5 = 450 to get a5 = 90

So s9 = a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 = (a1 + a2 + a8 + a9) + (a3 + a4 + a6 + a7) + a5 = 9 a5 = 810

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