(12ⁿ-3ⁿ)/(2ⁿ+1)=3ⁿ*(4ⁿ-1)/(2ⁿ+1)=3ⁿ*(2²ⁿ-1)/(2ⁿ+1)=
=3ⁿ*(2ⁿ+1)*(2ⁿ-1)/(2ⁿ+1)=3ⁿ*(2ⁿ-1).
5х-12х-42=13-х-1
5х-12х+х=13-1+42
-6х=54
х=-9
X^2+6x+9=2x+6
x^2+4x+3=0;
D=4;
x1=-4+2/2=-1; x2=-3
Ответ: x1=-1; x2=-3
5x^2+10x-x+3(x^2+16)=2(4x^2+12x+9)-8= 5x^2+10x-x+3x^2+48-8x^2-24x-18+8=-14x-10