Question

solve the system.

{-5x - y = 21
3x - 4y +5z = -8
-3x -z = 12

Answer 1

are there any z's in the 1st equations or any y's in the 3rd equation ?

Answer 2

@nsschwab23 .....???

Answer 3

no there is not

Answer 4

y=-5x-21 ---> y=-1
3x+20x+84-15x-60=-8 ---> x=-4
z=-3x-12 -----> z=0

Answer 5

-5x - y = 21 --> -y = 5x + 21 --> y = -5x - 21
-3x - z = 12 --> -z = 3x + 12 --> z = - 3x - 12
now sub these into 2nd equation
3x - 4y + 5z = - 8
3x - 4(-5x - 21) + 5(-3x - 12) = - 8
3x + 20x + 84 - 15x - 60 = - 8
8x + 24 = - 8
8x = -8 - 24
8x = - 32
x = - 32/8 = - 4
now sub -4 in for x
y = - 5x - 21
y = - 5(-4) - 21
y = 20 - 21
y = -1
go ahead and sub -4 into the 3rd equation
z = -3x - 12
z = -3(-4) - 12
z = 12 - 12
z = 0
check...
3x - 4y + 5z = -8
3(-4) - 4(-1) + 5(0) = - 8
-12 + 4 + 0 = - 8
-8 = -8 (correct)
ANSWER : x = - 4, y = - 1, z = 0

Answer 6

thank you for the help

Answer 7

your welcome....glad to help :)