Question

tìm x ; y

\(\frac{x}{7}\)= \(\frac{y}{3}\) và x - y =20

3\(^{x-3}\). 9 = 729

\(\frac{5}{6}\)+ 3 .| x - \(\frac{1}{2}\)| = \(\frac{7}{3}\)

Answer 1

\(\frac{x}{7}=\frac{y}{3}=\frac{x-y}{7-3}=\frac{20}{4}=5\)

\(\frac{x}{7}=5\Rightarrow x=35\)

\(\frac{y}{3}=5\Rightarrow y=15\)

tíc mình nha

Answer 2

3 bài à

1/  ta có x/7 = y/3 và x-y=20

ADTCDTSBN

x/7=y/3 = x-y/ 7-3 = 20/4= 5

Suy ra

x/7=5 => x=7.5= 35

y/3=5=> y= 3.5 = 15

Vậy x = 35 và y=15

Answer 3

2/ 3^x-3.9= 729

3^x-3 . 3²=(3²)³

x-3 .2=6

x-3 = 6:2 

x-3= 3

x= 3+3 

x=6

Answer 4

\(\frac{x}{7}=\frac{y}{3}\)và x-y=20

áp dụng t/c dãy tỉ số bằng nhau ta có:

\(\frac{x}{7}=\frac{y}{3}=\frac{x-y}{7-3}=\frac{20}{4}=5\)

vì \(\frac{x}{7}=5\)=>x=5.7=35

\(\frac{y}{3}=5\)=>y=3.5=15

vậy x=35;y=15

Answer 5

a]   áp dụng tính chất của dãy tỉ số bằng nhau ta có:

\(\frac{x}{7}=\frac{y}{3}=\frac{x-y}{7-3}=\frac{20}{4}=5\)

\(\frac{x}{7}=5\Rightarrow x=5.7=35;\frac{y}{3}=5\Rightarrow y=5.3=15\)

b,     

\(3^{x-3}.9=729\)

\(3^{x-3}.3^2=3^6\)

\(\Rightarrow x-3+2=6\)

\(x-3=6-2\)

\(x-3=4\)

\(x=4+3=7\)

c

\(\frac{5}{6}+3.|x-\frac{1}{2}|=\frac{7}{3}\)

\(3.|x-\frac{1}{2}|=\frac{7}{3}-\frac{5}{6}\)

\(3.|x-\frac{1}{2}|=\frac{3}{2}\)

\(|x-\frac{1}{2}|=\frac{3}{2}:3=\frac{1}{2}\)

\(\left(+\right)x-\frac{1}{2}=\frac{1}{2}\Rightarrow x=\frac{1}{2}+\frac{1}{2}=1\)

\(\left(+\right)x-\frac{1}{2}=\frac{-1}{2}\Rightarrow x=\frac{-1}{2}+\frac{1}{2}=0\)

Answer 6

\(3^{x-3}\).9=729

=>\(3^{x-3}\)= 729:9

\(3^{x-3}\)=81

=>\(3^{x-3}=3^4\)

=>x-3=4

=>x=4+3

=>x=7

vậy x=7