21-25-70+30+70 =

{70+30}-{70+25-21}=100-74

=36

a) 12/16 = -x/4    <=> 12.4=-x.16   <=> -16x=48    <=> x= -48/16=-3

12/16=21/y    <=> 12.y=16.21    <=>12y=336     <=> y= 336:12    <=> y=28

b)   3/x =-42/70    <=>   -42.x=70.3      <=>  -42x=210    <=> x=210/(-42)=-5

y/35=-42/70   <=> 70.y=-42.35       <=>70y=-1470     <=>  y= -1470: 70=-21

a) \(\left(x-2\right)\left(y-3\right)=14\\ \left(x-2\right)\left(y-3\right)=1\cdot14=14\cdot1=2\cdot7=7\cdot2=\left(-1\right)\left(-14\right)=\left(-14\right)\left(-1\right)=\left(-2\right)\left(-7\right)=\left(-7\right)\left(-2\right)\)

Ta có bảng sau:

Vậy \(\left(x;y\right)\in\left\{\left(3;17\right);\left(16;4\right);\left(4;10\right);\left(9;5\right);\left(1;-11\right);\left(-12;2\right);\left(0;-4\right);\left(-5;1\right)\right\}\)

b) \(\left(x-5\right)\left(y+5\right)=21\\ \left(x-5\right)\left(y+5\right)=1\cdot21=21\cdot1=3\cdot7=7\cdot3=\left(-1\right)\left(-21\right)=\left(-21\right)\left(-1\right)=\left(-3\right)\left(-7\right)=\left(-7\right)\left(-3\right)\)

Ta có bảng sau:

Vậy \(\left(x;y\right)\in\left\{\left(6;16\right);\left(26;-4\right);\left(8;2\right);\left(12;-2\right);\left(4;-26\right);\left(-16;-6\right);\left(2;-12\right);\left(-2;-8\right)\right\}\)

c) \(x\left(y-1\right)-6\left(y-1\right)=25\\ \left(x-6\right)\left(y-1\right)=25\\ \left(x-6\right)\left(y-1\right)=1\cdot25=25\cdot1=5\cdot5=\left(-1\right)\left(-25\right)=\left(-25\right)\left(-1\right)=\left(-5\right)\left(-5\right)\)

Ta có bảng sau:

Vậy \(\left(x;y\right)\in\left\{\left(7;26\right);\left(31;2\right);\left(11;6\right);\left(5;-24\right);\left(-19;0\right);\left(1;-4\right)\right\}\)

»Ҫɦέɱ¹sէ«

1    .  x=\(\frac{15}{4};y=\frac{35}{4}\)

2     .  x = -15 ; y = -21

x=3   y=(-7)  hoặc ngược lại

Bạn giúp ko có phép tính ak ???

x;y= 13;21 nha

Hok tốt