設有兩等差級數，它們的比是（2n+3):(3n+2),試求它們的前11 項之和的比

answer:

(2n+3)(3n+2)

6n^2 + 4n + 9n +6

= 6n^2 + 13n + 6

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second option

step-by-step explanation:

the measures of a triangle equal 180. use that to find x.

2x+3x+4x=180

9x=180

9x/9=180/9

x=20

now you know x, you know angle a is 40°, angle b is 60°, angle c is 80°.

because angle a is 40°, the first option doesn't work.

because angle b is 60°, the second option does work.

when you add angle a and b, you get 100°. complementary means it equals 90°, so the third option doesn't work.

when you add angle a and c, you get 120°, which is not 100.

the answer is 15 to your question