Question

Solve for
3x + 6Y - 9z = 3
5x - 7y + 10z = -4
11x +4y - 6z = 2

Answer 1

take the first equation, and the third equation.
mulitiply the first by 2, and the third by 3.

6x+12y-18z=6
33x+12y-18z=6

that implies that x is zero.
then the first and second

6y-9z=3
-7y+10z=-4
multply the first by 10, the second by 9
60y-90z=30
-63y+90z=-36
add,
-3y=6 or y=-2

solve for z in any equation, check your answers.

Answer 2

Since you don't specify which method, let's use good ol' elimination.

#1x2 ---> 6x+12y-18z=6
#3x3 ---> 33x+12y-18z=6
subtract, by luck both z and y disappear
x = 0

#2x3 ---> 15x-21y+30z=-12
#3x5 ---> 55x+20y-30z=10
add
70x-y=-2 but x=0, so
y = 2

sub back into #3 to get z = 1

x=0
y=2
z=1

Answer 3

2x^3(2x^2+4x+3)