4,2÷0,21=300÷х
4,2/0,21=300/х
х =300×0,21/4,2=63/4,2=15
ответ:х=15
12 = 2 * 2 * 3
18 = 2 * 3 * 3
НОД (12; 18) = 2 * 3 = 6
18 = 2 * 3 * 3
12 = 2 * 2 * 3
НОК (12; 18) = 2 * 3 * 3 * 2 = <span>36
</span> 13 = 13
39 = 3 * 13
НОД (13; 39) = 13
39 = 3 * 13
13 = 13
НОК (13; 39) = 3 * 13 = <span>39
</span>11 = 11
15 = 3 * 5
НОД (11; 15) = 1
15 = 3 * 5
11 = 11
НОК (11; 15) = 3 * 5 * 11 = <span>165</span>
x + y = 5
2y^2 - 5x = 8
Решение
x = 5 - y
2y^2 - 5( 5 - y ) = 8
2y^2 - 25 + 5y - 8 = 0
2y^2 + 5y - 33 = 0
D = 25 + 264 = 289 = 17^2
y1 = ( - 5 + 17 ) : 4 = 3
y2 = ( - 5 - 17 ) : 4 = - 5,5
x1 = 5 - 3 = 2
x2 = 5 + 5,5 = 10,5
Ответ ( 2 ; 3 ) ; ( 10,5 ; - 5,5 )