3x=4y-21
=> x=\(\frac{4y-21}{3}=\frac{4y}{3}-7\)
x < 10 => \(\frac{4y-21}{3}< 10\)=> 4y-21 < 30 => 4y < 51 => y<51/4=12,75
Mà 4y phải chia hết cho 3 => y=3; 6; 9; 12
+/ y=3 => x=-3
+/ y=6 => x=1
+/ y=9 => x=5
+/ y=12 => x=9
(3-4)x=-21
-x=-21
=>x=21
mấy bn kia chép giỏi quá
( 3 - 4 ) x = -21
-x = -21
= > x = 21
3x - 4x = -21
( 3 - 4 )x = -21
-x = -21
=> x = 21
a
1+1=2
2+3+4+5
= (1+1) × (1+1+1) × .....
=14
=> 14số 1