Câu hỏi của Phạm NI NA

Question

$\left(\sqrt{28}-\sqrt{12}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

$\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

Mysterious Person · Accepted Answer

$\left(\sqrt{28}-\sqrt{12}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

= $14-2\sqrt{21}-7+2\sqrt{21}$ = $7$

$\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

= $33-3\sqrt{22}-11+3\sqrt{21}$ = $22-3\sqrt{22}+3\sqrt{21}$

Câu trả lời:

$\left(\sqrt{28}-\sqrt{12}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

= $14-2\sqrt{21}-7+2\sqrt{21}$ = $7$

$\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

= $33-3\sqrt{22}-11+3\sqrt{21}$ = $22-3\sqrt{22}+3\sqrt{21}$

qwerty · Answer

Mình sẽ làm cụ thể một tí nhé:

a) $\left(\sqrt{28}-\sqrt{12}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

$=\left(2\sqrt{7}-2\sqrt{3}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

$=\left(\sqrt{7}-2\sqrt{3}\right)\sqrt{7}+2\sqrt{21}$

$=7-2\sqrt{21}+2\sqrt{21}$

$=7$

b) $\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

$=\left(3\sqrt{11}-3\sqrt{2}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

$=\left(2\sqrt{11}-3\sqrt{2}\right)\sqrt{11}+3\sqrt{21}$

$=22-3\sqrt{22}+3\sqrt{21}$

Câu trả lời:

Mình sẽ làm cụ thể một tí nhé:

a) $\left(\sqrt{28}-\sqrt{12}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

$=\left(2\sqrt{7}-2\sqrt{3}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}$

$=\left(\sqrt{7}-2\sqrt{3}\right)\sqrt{7}+2\sqrt{21}$

$=7-2\sqrt{21}+2\sqrt{21}$

$=7$

b) $\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

$=\left(3\sqrt{11}-3\sqrt{2}-\sqrt{11}\right)\sqrt{11}+3\sqrt{21}$

$=\left(2\sqrt{11}-3\sqrt{2}\right)\sqrt{11}+3\sqrt{21}$

$=22-3\sqrt{22}+3\sqrt{21}$