Question

Answer 1

4:

a: x/4=5/y

=>xy=20

=>\(\left(x,y\right)\in\left\{\left(1;20\right);\left(20;1\right);\left(-1;-20\right);\left(-20;-1\right);\left(2;10\right);\left(10;2\right);\left(-2;-10\right);\left(-10;-2\right);\left(4;5\right);\left(5;4\right);\left(-5;-4\right);\left(-4;-5\right)\right\}\)

b: x/y=28/35

=>x/y=4/5

=>x/4=y/5=k

=>x=4k; y=5k

=>\(\left(x,y\right)\in\left\{\left(4k;5k\right);k\in Z\right\}\)

 

5:

a: a/b=36/45

=>a/b=4/5

BCNN(a,b)=300

=>300 chia hết cho a và 300 chia hết cho b

mà a/b=4/5

nên a=60; b=75

b: a/b=21/35

=>a/b=3/5

ƯCLN(a,b)=30

=>a chia hết cho 30 và b chia hết cho 30

mà a/b=3/5

nên a=90; b=150