(4-y)²-y(y-1)=16-8y+y²-y²+y=16-7y
при y=-1/9
16-7*(-1/9)=16+7/9=16 7/9
Ответ: 16 7/9
-5х²+15х+5х²-10х+5=87
5х=87-5
5х=82
х=16,4
<span>{y= 2x -1
{y=x+3
-------------
0=x-4
x=4
y=4+3=7
ответ (4;7)</span>
5a>9 a>9/5=1.8
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Cos(15-45) + 2sin(-45)*sin(15) = cos(30) - 2sin(45)*sin(45 - 30)
cos(30) = √3/2
sin(45) = √2/2
sin(45 - 30) = sin45*cos30 - sin30*cos45 = (√2/2)*(√3/2) - √2/4 = (√6 - √2)/4
√3/2 - (√2/2)*(√6 - √2)/2 = √3/2 - (√2*(√6 - √2)/4) = (2√3 - 2√32 + 2)/4 = 2/4 = 1/2