Chu vi tam giac đều =27 cm

ma 9 + 9 + 9 =27

=> canh tam giac đều = 9cm

\(x+1+x+2+x+3+x+4=34\\ \left(x+x+x+x\right)+\left(1+2+3+4\right)=34\\ 4x+10=34\\ 4x=34-10\\ 4x=24\\ x=6\)

\(\text{a},=6\sqrt{2}-7\sqrt{2}+9\sqrt{2}=8\sqrt{2}\\ b,=5\sqrt{5}-4\sqrt{5}-12\sqrt{5}+12\sqrt{5}=\sqrt{5}\\ c,=\sqrt{17-3\sqrt{16.2}}+\sqrt{17+3\sqrt{16.2}}=\sqrt{17-12\sqrt{2}}+\sqrt{17+12\sqrt{2}}=\sqrt{\left(\sqrt{6}-\sqrt{2}\right)^2}+\sqrt{\left(\sqrt{6}+\sqrt{2}\right)^2}\)

=I\(\sqrt{6}-\sqrt{2}\)I+I\(\sqrt{6}+\sqrt{2}\)I=\(\sqrt{6}-\sqrt{2}+\sqrt{6}+\sqrt{2}=2\sqrt{6}\)

\(\text{a},=\sqrt{9}.\sqrt{\left(x-5\right)^2}=3.\left(x-5\right)=3x-15\\ b,=\sqrt{x^2}.\sqrt{\left(x-2\right)^2}=x\left(x-2\right)=x^2-2x\\ c,=3\sqrt{x}+5\sqrt{x}-4\sqrt{x}=4\sqrt{x}\)

\(=\left(\sqrt{x}-\sqrt{y}\right)\left(x+\sqrt{xy}+y\right)\)

\(\text{a},x-45=0:27\\ x-45=0\\ x=45\\ b,34-x=42:21\\ 34-x=2\\ x=32\\ c,x\left(2+3\right)=1505\\ 5x=1505\\ x=301\\ d,\left(x-1\right)=0ho\text{a}cx-8=0\\ x=1;x=8\)

3/4+2/3=\(\dfrac{3.3+2.4}{4.3}=\dfrac{9+8}{12}=\dfrac{17}{12}\)                       3/5+7/10=\(\dfrac{3.2+7}{10}=\dfrac{13}{10}\)            1/4+7/6=\(\dfrac{6+7.4}{24}=\dfrac{6+28}{24}=\dfrac{17}{12}\)

2/3-2/7=\(\dfrac{2.7-2.3}{21}=\dfrac{14-6}{21}=\dfrac{8}{21}\)                        3/4-5/12=\(\dfrac{3.3-5}{4.3}=\dfrac{1}{3}\)                        5/6-2/9=\(\dfrac{5.9-2.6}{54}=\dfrac{45-12}{54}=\dfrac{33}{54}=\dfrac{11}{18}\)

2+5/7=\(\dfrac{2.7+5}{7}=\dfrac{14+5}{7}=\dfrac{29}{7}\)                             

13/5-2=\(\dfrac{13-2.5}{5}=\dfrac{13-10}{5}=\dfrac{3}{5}\)                           

3-3/8=\(\dfrac{3.8-3}{8}=\dfrac{24-3}{8}=\dfrac{21}{8}\)

1/2+1/3+1/6=\(\dfrac{6+4+2}{12}=\dfrac{12}{12}=1\)                   

5/12+5/6-3/4\(=\dfrac{5+5.2-3.3}{12}=\dfrac{5+10-9}{12}=\dfrac{6}{12}=\dfrac{1}{2}\)                 

1-(1/5+1/2)=\(1-\left(\dfrac{2+5}{10}\right)=1-\dfrac{7}{10}=\dfrac{10-7}{10}=\dfrac{3}{10}\)

Bài 102: Tính bằng cách thuận tiện nhất

a) 2/9+1/5+7/9+4/5 \(=\left(\dfrac{2}{9}+\dfrac{7}{9}\right)+\left(\dfrac{1}{5}+\dfrac{4}{5}\right)=\dfrac{9}{9}+\dfrac{5}{5}=1+1=2\)

b) 1/12+3/16+5/12+5/16 \(=\left(\dfrac{1}{12}+\dfrac{5}{12}\right)+\left(\dfrac{3}{16}+\dfrac{5}{16}\right)=\dfrac{6}{12}+\dfrac{8}{16}=\dfrac{1}{2}+\dfrac{1}{2}=\dfrac{2}{2}=1\)

 20 lớn hơn hoặc bằng B(12) lớn hơn hoặc bằng 50 = {24, 36, 48}

a, xx'//yy'

Vì có góc tax =góc aby=110 độ

ma hai góc vị trí đồng vị 

=> xx'//yy'

b, xx' ⊥ a

Ta có yy' ⊥ a ( gia thiết )

ma xx' //yy' ( cmt)

=> xx' ⊥ a