Maths problem: how to do, thanks?

2020-08-01 7:54 pm

回答 (1)

2020-08-01 8:19 pm
✔ 最佳答案
Let its 1st term = a, common ratio = r 
T(1) + T(2) = 1
a + ar = 1
a(1+r) = 1 . . . . . . . . . . . . . ①

T(6) + T(7) = -32
ar⁵ + ar⁶ = -32
ar⁵(1+r) = -32 . . . . . . . . . . ②


 ②/①:  r⁵ = -32 => r = -2

Put r = -2 into ① : a(1+-2) = 1
∴ 1st term, a = -1 


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