c,Có x=\(\frac{1}{2}\left(\sqrt{\frac{1-a}{a}}-\sqrt{\frac{a}{1-a}}\right)\left(0< a< 1\right)\)

<=> \(x=\frac{1}{2}\left(\frac{\sqrt{1-a}}{\sqrt{a}}-\frac{\sqrt{a}}{\sqrt{1-a}}\right)\) (vì 0<a<1)

<=>\(x=\frac{1}{2}.\frac{\sqrt{1-a}^2-\sqrt{a}^2}{\sqrt{a}.\sqrt{1-a}}=\frac{1}{2}.\frac{1-a-a}{\sqrt{a\left(1-a\right)}}=\frac{1}{2}.\frac{1-2a}{\sqrt{a\left(1-a\right)}}=\frac{1-2a}{2\sqrt{a\left(1-a\right)}}\)(1)

<=> 1+x²=1+\(\frac{1}{4}.\frac{\left(1-2a\right)^2}{a\left(1-a\right)}\)= \(\frac{4a\left(1-a\right)+\left(1-2a\right)^2}{4a\left(1-a\right)}\)

<=> 1+x²=\(\frac{4a-4a^2+1-4a+4a^2}{4a\left(1-a\right)}=\frac{1}{4a\left(1-a\right)}\)>0

<=> \(\sqrt{1+x^2}=\frac{1}{2\sqrt{a\left(1-a\right)}}\) (2)

Thay (1),(2) vào C có:

C= \(\frac{2a.\frac{1}{2\sqrt{a\left(1-a\right)}}}{\frac{1}{2\sqrt{a\left(1-a\right)}}-\frac{1-2a}{2\sqrt{a\left(1-a\right)}}}=\frac{\frac{a}{\sqrt{a\left(1-a\right)}}}{\frac{1-1+2a}{2\sqrt{a\left(1-a\right)}}}=\frac{\frac{a}{\sqrt{a\left(1-a\right)}}}{\frac{2a}{2\sqrt{a\left(1-a\right)}}}=1\)

Vậy C=1

25 - 9y^2 

= 5^2 - (3y)^2

= (5 - 3y)(5+3y) 

a, vì AT là tia phân giác của góc xAB nên At cắt yy'

b, Vì góc xAB=70 nên xAt=tAB=\(\frac{xAB}{3}\)=\(\frac{70}{2}\)= 35

góc tAB và góc ACB là hai góc kề bù => ACB=180-tAB= 180=35=145

Có \(\frac{\sqrt{15}-\sqrt{5}}{\sqrt{3}-1}+\sqrt{\left(2-\sqrt{5}\right)^2}-2\sqrt{5}\)

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

=\(\sqrt{5}-2+\sqrt{5}-2\sqrt{5}=-2\)

2x2=4

3x3=9

6x6=36

Ủng hộ nha

gấp 2 lần

tui

k tui nha

                      Ta có :

                      \(\left|x+74\right|-\left|-318\right|=\left|-20\right|\)

                      \(\left|x+74\right|-318=20\)

                      \(\left|x+74\right|=20+318=338\)

                   \(\Rightarrow\orbr{\begin{cases}x+74=338\\x+74=-338\end{cases}}\Rightarrow\orbr{\begin{cases}x=338-74\\x=-338-74\end{cases}}\)

                  \(\Rightarrow\orbr{\begin{cases}x=264\\x=-412\end{cases}}\)

                 Ủng hộ mk nha !!! ^_^

x:3-7,2=1,56

x:3     =1,56+7,2

x:3     =8,76

x        =8,76 . 3

x        = 26,28

(Lưu ý : dấu chấm có nghĩa là dấu nhân)

x=18,5 - (13,26 - 5,6)

x=10,84