a) Quy đồng bỏ mẫu rồi giai pt ta đc : \(\orbr{\begin{cases}x=0\\x=1\end{cases}}\)

b)\(x=1\)

Con bai 2 thi sao a

3(2x+y)-2(3x-2y)=3.19-11.2

6x+3y-6x+4y=57-22

7y=35

y=5

thay vào :

2x+y=19

2x+5=19

2x=14

x=7

2/ x²+21x-1x-21=0

x(x+21)-1(x+21)=0

(x+21)(x-1)=0

TH1 x+21=0

x=-21

TH2 x-1=0

x=1

vậy x = {-21} ; {1}

3/ x⁴-16x²-4x²+64=0

x²(x²-16)-4(x²-16)=0

(x²-16)-(x²-4)=0

TH1 x²-16=0

x²=16

<=>x=4;-4

TH2 x²-4=0

x²=4

x=2;-2

Bài 1 : 

\(\hept{\begin{cases}2x+y=19\\3x-2y=11\end{cases}\Leftrightarrow\hept{\begin{cases}4x+2y=38\\3x-2y=11\end{cases}\Leftrightarrow\hept{\begin{cases}7x=49\\2x+y=19\end{cases}}}}\)

\(\Leftrightarrow\hept{\begin{cases}x=7\\2x+y=19\end{cases}}\)Thay vào x = 7 vào pt 2 ta được : 

\(14+y=19\Leftrightarrow y=5\)Vậy hệ pt có một nghiệm ( x ; y ) = ( 7 ; 5 )

Bài 2 : 

\(x^2+20x-21=0\)

\(\Delta=400-4\left(-21\right)=400+84=484\)

\(x_1=\frac{-20-22}{2}=-24;x_2=\frac{-20+22}{2}=1\)

Bài 3 : Đặt \(x^2=t\left(t\ge0\right)\)

\(t^2-20t+64=0\)

\(\Delta=400+4.64=656\)

\(t_1=\frac{20+4\sqrt{41}}{2}\left(tm\right);t_2=\frac{20-4\sqrt{41}}{2}\left(ktm\right)\)

Theo cách đặt : \(x^2=\frac{20+4\sqrt{41}}{2}\Rightarrow x=\sqrt{\frac{20+4\sqrt{41}}{2}}=\frac{\sqrt{20\sqrt{2}+4\sqrt{82}}}{2}\)

Đặt \(\frac{x-2}{x-1}=a;\frac{x+2}{x+1}=b\) ta có: \(pt\Leftrightarrow10a^2+b^2-11ab=0\)

\(\Leftrightarrow10a^2-10ab-ab+b^2=0\Leftrightarrow\left(a-b\right)\left(10a-b\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}a=b\\10a=b\end{cases}}\)

TH1: \(\frac{x-2}{x-1}=\frac{x+2}{x+1}\)

TH2: \(10.\frac{x-2}{x-1}=\frac{x+2}{x+1}\)

Từ đó em có thể làm tiếp nhé.

jup mk vs cac ty oi

a: 11x+4=-3/2

=>\(11x=-\dfrac{3}{2}-4=-\dfrac{11}{2}\)

=>\(x=-\dfrac{1}{2}\)

b: \(x^2-9+2\left(x-3\right)=0\)

=>\(\left(x-3\right)\left(x+3\right)+2\left(x-3\right)=0\)

=>\(\left(x-3\right)\left(x+3+2\right)=0\)

=>(x-3)(x+5)=0

=>\(\left[{}\begin{matrix}x-3=0\\x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-5\end{matrix}\right.\)

c: \(\dfrac{x-3}{5}+\dfrac{1+2x}{3}=6\)

=>\(\dfrac{3\left(x-3\right)+5\left(2x+1\right)}{15}=6\)

=>\(3x-9+10x+5=90\)

=>13x-4=90

=>13x=94

=>\(x=\dfrac{94}{13}\)

d: \(\dfrac{2}{x+1}-\dfrac{1}{x-2}=\dfrac{3x-11}{\left(x+1\right)\left(x-2\right)}\)(ĐKXĐ: \(x\notin\left\{-1;2\right\}\))

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

=>3x-11=2x-4-x-1

=>3x-11=x-5

=>2x=6

=>x=3(nhận)

Câu 10: A

Câu 11: A

Câu 12: C

Câu 13: A

Câu 15: B

Câu 16: C

Câu 17: B

Câu 18: D

a: \(\Leftrightarrow\left(4x+14\right)^2-\left(3x+9\right)^2=0\)

=>(4x+14+3x+9)(4x+14-3x-9)=0

=>(7x+23)(x+5)=0

=>x=-23/7 hoặc x=-5

\(a,\\ \Leftrightarrow7x^2+58x+115=0\\ \Leftrightarrow\left(x+5\right)\left(7x+23\right)=0\\ \Leftrightarrow\left\{{}\begin{matrix}x+5=0\\7x+23=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-5\\x=-\dfrac{23}{7}\end{matrix}\right.\)

\(b,\\ \Leftrightarrow\left[\left(x+1\right)\left(x+5\right)\right]\left[\left(x+3\right)\left(x+4\right)\right]=0\\ \Leftrightarrow\left(x^2+6x+5\right)\left(x^2+6x+8\right)=0\\ \LeftrightarrowĐặt.x^2+6x+5=a\\ \Leftrightarrow a=a\left(a+3\right)=10\\ \Leftrightarrow a^2+3a-10=0\\ \Leftrightarrow\left(a+5\right)\left(a-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}a=-5\\a=2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x^2+6x+5=-5\\x^2+6x+5=2\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x^2+6x+10=0\\x^2+6x+3=0\end{matrix}\right.\\ \left(Vô.n_o\Delta=36-40=-4< 0\right)\) 

\(\Leftrightarrow\left[{}\begin{matrix}x=-3+\sqrt{6}\\x=-3-\sqrt{6}\end{matrix}\right.\)

cais cuối là :

\(\Leftrightarrow x=1\left(ktm\right)\)

vậy pt ko có nghiệm á