r 2- 12r – 28 = 0 $r 2- 12r - 28 = 0$

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Mathematics Euphemia 4 years 2021-09-03T08:13:50+00:00 2021-09-03T08:13:50+00:00 1 Answers 4 views 0

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Captcha* Giải phương trình 1 ẩn: x + 2 - 2(x + 1) = -x . Hỏi x = ? ( )

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Doris · Answer 1 · 2021-09-03T08:15:20+00:00

Doris

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2021-09-03T08:15:20+00:00 September 3, 2021 at 8:15 am

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Answer:

Step-by-step explanation:

r² – 12r – 28 = 0

r² – (14 – 2)r – 28 = 0

r² – 14r + 2r – 28 = 0

r ( r – 14 ) + 2 ( r – 14 ) = 0

( r – 14) ( r + 2 ) = 0

Either

r – 14 = 0

r = 14

or

r + 2 = 0

r = -2

therefore r = – 2 or 14