5)=х^2-5х+3х-15-х^2+23=
=-2х+8
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6)
34х-30х=-27+15
4х=-8
х=-8÷4
х=-2
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4)
(а+5)^2=а^2+10а+25
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5)=а^12/а^13=1/а=1÷1/5=5
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6)49-х^2=(7-х)(7+х)
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7)=(у-4)^2/(у-4)(у+4)=
=(у-4)/(у+4)
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8)9бх-3б^2=3б(3х-б)
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9)6х+9-6х-10=-1
-1=-1
корень 0
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10)у=2х+6
15х+2(2х+6)=7
15х+4х+12=7
19х=7-12
19х=-5
х=-5/19
у=2×(-5/19)+6=-10/19+6=5 9/19
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11) составим систему
х+у=75
х-у=23
метод сложения
х+х+у-у=75+23
2х=98
х=49
у=75-х=75-49=26