1. are visiting
2. don't go
3. are not going to work
4. Does Mary have
5. meet

are visting

don't go

won't work

Does Mary have

meet

1. are visiting 

2. don't go

3. aren't going to work

4. Does Mary have

5. meet

\(A=\sqrt{3-\sqrt{5}}-\sqrt{4-\sqrt{15}}+\sqrt{6-3\sqrt{3}}\)

\(=\dfrac{1}{\sqrt{2}}\cdot\left(\sqrt{6-2\sqrt{5}}-\sqrt{8-2\sqrt{15}}+\sqrt{12-6\sqrt{3}}\right)\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{5}-1-\sqrt{5}+\sqrt{3}+3-\sqrt{3}\right)\)

=2/căn 2=căn 2

\(B=\sqrt{4-\sqrt{7}}-\sqrt{14-5\sqrt{3}}-\sqrt{5+\sqrt{21}}\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{8-2\sqrt{7}}-\sqrt{28-10\sqrt{3}}-\sqrt{10+2\sqrt{21}}\right)\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{7}-1-5+\sqrt{3}-\sqrt{7}-\sqrt{3}\right)\)

=-6/căn 2=-3căn2

\(C=\sqrt{11-6\sqrt{2}}-\sqrt{6-4\sqrt{2}}+\sqrt{7-2\sqrt{6}}\)

=3-căn 2-2+căn 2+căn 6-1

=căn 6

\(D=\sqrt{6-\sqrt{11}}-\sqrt{10+3\sqrt{11}}+2\sqrt{2}-1\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{12-2\sqrt{11}}-\sqrt{20+6\sqrt{11}}\right)+2\sqrt{2}-1\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{11}-1-\sqrt{11}-3\right)+2\sqrt{2}-1\)

=-1

\(F=\sqrt{6+3\sqrt{3}}-\sqrt{2+\sqrt{3}}+\sqrt{6-4\sqrt{2}}\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{12+6\sqrt{3}}-\sqrt{4+2\sqrt{3}}\right)+2-\sqrt{2}\)

=1/căn 2(3+căn 3-căn 3-1)+2-căn 2

=căn 2+2-căn 2

=2

15:

1:

góc A=2*góc B

mà góc A+góc B=180-60=120 độ

nên góc A=80 độ; góc B=40 độ

2: 

a: Xet ΔAMB và ΔAMC có

AM chung

MB=MC

AB=AC

=>ΔAMB=ΔAMC

b: Xét ΔMBD và ΔMCE có

MB=MC

góc MBD=góc MCE

BD=CE

=>ΔMBD=ΔMCE

=>MD=ME

c: ΔADE cân tại A

mà AN là phân giác

nên AN vuông góc DE

  chọn D

đk : x khác 1 ; -3 

\(\Rightarrow2x+6+4x-4=3x+11\Leftrightarrow3x=9\Leftrightarrow x=3\left(tm\right)\)

\(a))\Delta ABC:\)

\(\dfrac{AM}{AB}=\dfrac{AN}{AC}\left(do\dfrac{4}{12}=\dfrac{5}{15}\right).\\ \Rightarrow MN//BC\left(Talet\right).\)

\(b))\Delta ABC:MN//BC\left(cmt\right).\\ \Rightarrow\dfrac{MN}{BC}=\dfrac{AM}{AB}\left(Talet\right).\\ \Rightarrow MN=\dfrac{AM.BC}{AB}=\dfrac{4.21}{12}=7\left(cm\right).\)

2:

A=(x1-x2)^2-x1^2+x1(x1+x2)

=(x1-x2)^2+x1x2

=(x1+x2)^2-3x1x2

=(1/2)^2-3*(-1/4)=1/4+3/4=1