7х+6=3х
7x-3x=-6
4x=-6
x=(-6):4
x=-3/2
[b]x=-1,5[/b]
2)
3+4x=9x-11
4x-9x=-11-3
-5x=-14
x=(-14):(-5)
x=14/5
[b]x=2,8[/b]
3)
2(x+5)=9
2x+2*5=9
2x+10=9
2x=9-10
2x=-1
x=-1/2
[b]x=-0,5[/b]
4)
16/(x+3)=-8/11
пропорция
-8(х+3)=16*11
-8х-24=176
-8х=176+24
-8х=200
х=200:(-8)
[b]х=-25[/b]
5)
х^2-9=0
(x-3)(x+3)=0
x-3=0 или x+3=0
[b]x=3[/b] или [b]x=-3[/b]
6)
8х^2-72x=0
8x*(x-9)=0
x=0 или x-9=0
[b]x=0[/b] или [b]x=9[/b]
7)
x^2+11=12x
x^2-12x+11=0
D=(-12)^2-4*11=144-44=100
x_(1)=(12-10)/2; x_(2)=(12+10)/2
[b]x_(1)=1[/b]; [b]x_(2)=11[/b]
8)
5x^2-7x+2=0
D=(-7)^2-4*5*2=49-40=9
x_(1)=(7-3)/10; x_(2)=(7+3)/10
[b]x_(1)=2/5[/b]; [b]x_(2)=1[/b]
9)
x^2=t
x^4=t^2
t^2-4t+4=0
(t-2)^2=4
t=2
x^2=2
x^2-2=0
(x-sqrt(2))*(x+sqrt(2))=0
x-sqrt(2)=0 или x+sqrt(2)=0
[b]x=sqrt(2)[/b] или [b]x=-sqrt(2)[/b]