1)(5х2+8х-7)-(2х2-2х-12)=5x2+8x-7-2х2-12=3х2+6x-19
2)(2x-3)+(-2x2-5x-18)=2x-3-2x2-5x-18=-2x2-3x-21
3)(6a2-3a+11)-(-3a-a3+7)=6a2-3a+11+3a+a3-7=a3+6a2+11
4)(14ab-9a2-3b2)-(-3a2+5ab-4b2)=14ab-9a2-3b2+3a2-5ab+4b2=-7a2+9ab+b2
5)(7xy2-15xy+3x2y)+(30xy-8x2y)=7xy2-15xy+3x2y+30xy-8x2y=-5x2y+7xy2+15xy
6)(3/5m3n2-1/4mn2)-(-5/8n2m+7/10m3n2)=1;3/10m3n2+3/8mn2
<span>3/7x - 5/12 = -11/14x - 3/4
3/7x + 11/14x = -3/4 + 5/12
6/14x + 11/14x = -9/12 + 5/12
17/14x = - 4/12
x = -1/3 * 14/17
x = -14/51</span>
Ответ:Через 5 минут
1)5*6=30(м)
2)5*3=15(м)
3)30-15=15(м)