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Môn Toán Dâu 4 years 2020-10-13T14:02:52+00:00 2020-10-13T14:02:52+00:00 1 Answers 102 views 0

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

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Orla · Answer 1 · 2020-10-13T14:03:54+00:00

Orla

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2020-10-13T14:03:54+00:00 October 13, 2020 at 2:03 pm

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Đáp án:

Giải thích các bước giải:

$A = x + y + \frac{9}{x + y} + \frac{1}{x + y} = x + y + \frac{9}{x + y} + \frac{1}{x + \frac{8 - x^{2}}{4}}$

$A = x + y + \frac{9}{x + y} + \frac{4}{12 - (x - 2)^{2}}$

$12 - (x - 2)^{2} = 4 x + 4 y > 0 \to \frac{4}{12 - (x - 2)^{2}} \geq \frac{4}{12} = \frac{1}{3}$

$\to A \geq 2 \sqrt{\frac{9 (x + y)}{x + y}} + \frac{1}{3} = \frac{19}{3}$

$A_{m i n} = \frac{19}{3}$ khi $x = 2; y = 1$