6x²+21x-2x-7-(5x²-x+15x-3)=x²+2x+1
6x²+21x-2x-7-5x²+x-15x+3=<span>x²+2x+1
</span>6x²-5x<span>²-x</span>²+21x-2x+x-15x-2x=1-3+7
3x=5
x=5/3
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Y = <span>1+12х-9х²;
y '(x) = 12 - 18 x;
y'= 0;
12 - 18 x = 0;
- 18x = -12;
x = 12/18 = 2/3;
y(2/3) = 1 + 12/1 * 2/3 - 9/1 * (4/9) = 1 + 8 - 4 = 5</span>