Tìm x, y, z biết:
\(\dfrac{x-1}{2}=\dfrac{y+3}{4}=\dfrac{z-5}{6}\) và \(5z-3x-4y=50\)

2. I'm talking on the phone at the moment.
Am I talking on the phone at the moment?
3. He is running very fast.
He isn't running very fast.
4. Julia isn't baking a chocolate cake at the moment.
Is Julia baking a chocolate cake at the moment?
5. Tony and Kaity are helping the teacher right now.
Tony and Kaity aren't helping the teacher right now.

Giúp mình với ạ

Tìm x, y, z biết:
c, \(5x=8y=20z;x-y-z=3\)

- Vietnam
- America 
- England
- Brazil
- Australia 
- China
- Korea 
- Japan 
- France
- Malaysia
- ...

Bài 7:
\(1+3+3^2+...+\)\(3^{98}\)
= \(\left(1+3+3^2\right)+...+\left(3^{96}+3^{97}+3^{98}\right)\)
= \(\left(1+3+3^2\right)+...+3^{96}.\left(1+3+3^2\right)\)
= 13+... + \(3^{96}\). 13 chia hết cho 13( đpcm)