\(\sqrt{10-2\sqrt{21}}=\sqrt{a}+\sqrt{b}\) thì a+b bằng bao nhiêu?
Viết \(\dfrac{18}{2\sqrt{3}-\sqrt{6}}=a\sqrt{3}-b\sqrt{6}\) thì a+b bằng bao nhiêu
Lời giải:
\(\frac{18}{2\sqrt{3}-\sqrt{6}}=\frac{18(2\sqrt{3}+\sqrt{6})}{(2\sqrt{3}-\sqrt{6})(2\sqrt{3}+\sqrt{6})}=\frac{36\sqrt{3}+18\sqrt{6}}{6}\)
\(=6\sqrt{3}+3\sqrt{6}\)
$\Rightarrow a=6; b=-3$
$\Rightarrow a+b=6+(-3)=3$
nếu \(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\) thì a - b = ?
bài này a,b phải nguyên thì may ra lm đc
\(\sqrt{10-2\sqrt{21}}=\sqrt{\left(\sqrt{7}-\sqrt{3}\right)}\)
=> a=7; b=3
a-b=4
nếu \(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\)
thì a-b=?
\(\sqrt{10-2\sqrt{21}}=\sqrt{3-2\sqrt{3}.\sqrt{7}+7}=\sqrt{7}-\sqrt{3}\Rightarrow a-b=4\)
Hoàng Anh Tú câu này dễ òm mà , giải mò cái j
Nếu \(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\)với \(a,b\in Z\) thì a - b = ?
1) Rút gọn:
a) A = \(\sqrt{5-2\sqrt{3-\sqrt{3}}}-\sqrt{3+\sqrt{3}}+\sqrt{2+\sqrt{3}}\)
b) B = \(\sqrt{13+\sqrt{2}+5\sqrt{1+2\sqrt{2}}}+\sqrt{13+\sqrt{2}+5\sqrt{1+2\sqrt{2}}}\)
c) C = \(\dfrac{\sqrt{21+3\sqrt{5}}+\sqrt{21-3\sqrt{5}}}{\sqrt{21}+6\sqrt{11}}+\sqrt{11-6\sqrt{2}}\)
d) D = \(\left(\sqrt{8+2\sqrt{10+2\sqrt{5}}}+\sqrt{8-2\sqrt{10+2\sqrt{5}}}\right).\sqrt{\dfrac{2+2\sqrt{5}}{2+\sqrt{5}}}\)
e) E = \(\dfrac{\left(27+10\sqrt{2}\right)\sqrt{27-10\sqrt{2}}-\left(27-10\sqrt{2}\right)\sqrt{27+10\sqrt{2}}}{\left(\sqrt{\sqrt{13}-3}+\sqrt{\sqrt{13}+3}\right):\sqrt{\sqrt{13}+2}}\)
\(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\) tính a-b= ?
\(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\)
\(\Leftrightarrow\sqrt{7-2\sqrt{7}\sqrt{3}+3}=\sqrt{a}-\sqrt{b}\)
\(\Leftrightarrow\sqrt{\left(\sqrt{7}-\sqrt{3}\right)^2}=\sqrt{a}-\sqrt{b}\)
\(\Leftrightarrow\sqrt{7}-\sqrt{3}=\sqrt{a}-\sqrt{b}\)
=>a=7;b=3 =>a-b=7-3=4
ko bik đúng ko
Nếu , với , thì ....
\(\sqrt{10-2\sqrt{21}}=\sqrt{\left(\sqrt{7}-\sqrt{3}\right)^2}\)
=\(\sqrt{7}-\sqrt{3}\)
=> a=7 và b=3
=> a-b=7-3=4
\(\sqrt{10-2\sqrt{21}}=\sqrt{7}-\sqrt{3}\)
\(\Rightarrow\sqrt{7}-\sqrt{3}=\sqrt{a}-\sqrt{b}\)
Suy ra \(\sqrt{7}=\sqrt{a}\rightarrow a=7\)
\(\sqrt{3}=\sqrt{3}\rightarrow b=3\)
Vậy \(a-b=7-3=4\)
\(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\)
Tìm hiệu a-b.
\(=\sqrt{7-2\sqrt{7.3}+3}=\sqrt{\left(\sqrt{7}-\sqrt{3}\right)^2}=\sqrt{7}-\sqrt{3}\)
a-b = 7 -3 =4
Neu \(\sqrt{10-2\sqrt{21}}=\sqrt{a}-\sqrt{b}\) va a,b thuoc Z thi a-b =?