1) <span>2х+у=15
y = 15 - 2x
x = (15 - y)/2
2) </span><span>у+6х=23
y = 23 - 6x
x = (23 - y)/6
3) </span><span>0,9х-2у=18
x = (18 + 2y)/0.9 = 20 + 2 2/9y
y = (0.9x - 18)/2 = 9/20 x - 9
4) </span><span>5у+2,5х=1
y = (1 - 2.5x)/5 = 0.2 - 0.5x
x = (1 - 5y)/2.5 = 0.4 - 2y</span>
18 * (11/12 - 8/9) : (5/14 + 2/7) = 7/9
1) 11/12 - 8/9 = 33/36 - 32/36 = 1/36
2) 5/14 + 2/7 = 5/14 + 4/14 = 9/14
3) 18 * 1/36 = 18/36 = 1/2
4) 1/2 : 9/14 = 1/2 * 14/9 = (1*7)/(1*9) = 7/9
6м-60дм
4м-40дм.
1) 60*40=2400дм в квадрате
2) 2*2=4 дм в квадрате
3 2400 дм в квадрате : 4 дм в квадрате= 600 плиток
Ответ:600 плиток