144a²-9+72a-144a²(144 уничтожаются)
остаётся:
72a-9
(1-2a)(1+2a+4a²)
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1) <span>12x²y+3xy=3ху(4х+1)
2) </span><span>(х-9)(х-3)-(х-8)(х+8)=-5
х</span>²-3х-9х+27-(х²-64)=-5
х²-3х-9х+27-х²+64+5=0
-12х+96=0
-12х=-96
х=8
3) <span>{4х-7у=1
</span><span>{2х+7у=11
</span>6х=12
х=2
4+7у=11
7у=7
у=1
1 1/4 - (1/15 + 1/10 + х) = 3/4
5/4 - (2/30 + 3/30 + х) = 3/4
- (5/30 + х) = 3/4 - 5/4
- (5/30 + х) = - 2/4
5/30 + х = 2/4
1/6 + х = 1/2
х = 1/2 - 1/6
х = 3/6 - 1/6
х = 2/6
х = 1/3
<u>проверка:</u>
1 1/4 - (1/15 + 1/10 + 1/3) = 3/4
5/4 - (2/30 + 3/30 + 10/30) = 3/4
5/4 - 15/30 = 3/4
5/4 - 1/2 = 3/4
5/4 - 2/4 = 3/4
3/4 = 3/4