a,$\frac{x-1}{5}$= $\frac{x+3}{3}$
⇔$\frac{3(x-1)}{15}$ =$\frac{5(x+3)}{15}$
⇒3x-3=5x+15
⇔3x-5x=15+3
⇔-2x=18
⇔x=-9
Vậy x=-9
b,$\frac{3}{x-1}$ =$\frac{21}{16}$
⇒(x-1).21=3.16
⇔21x-21=48
⇔21x=69
⇔x=23/7
Vậy x=23/7
c,$\frac{6,12}{3}$= $\frac{0,21}{x}$
⇒6,12x=3.0,21
⇔6,12x=0,63
⇔x=7/69
Vậy x=7/69
d,$\frac{x}{6}$= $\frac{7}{4}$
⇒4x=7.6
⇔4x=42
⇔x=21/2
Vậy x=21/2
e,$\frac{3}{x}$=$\frac{21}{17}$
⇔21x=3.17
⇔21x=51
⇔x=17/7
Vậy x=17/7
f, $\frac{2x+4}{7}$= $\frac{4x+2}{15}$
⇒(2x+4)15=(4x+2)7
⇔30x+60=28x+14
⇔2x=-46
⇔x=-23
Vậy x=-23
g,$\frac{2x+3}{24}$=$\frac{3x-1}{32}$
⇒(2x+3)32=(3x-1)24
⇔64x+96=72x-24
⇔-8x=-120
⇔x=15
Vậy x=15
