Solve the system of equations. ​ −5x−3y−9=0 4x−18y−54=0 y=? x=? ​

Question

Solve the system of equations.

−5x−3y−9=0
4x−18y−54=0
y=? x=?

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Vân Khánh 2 months 2021-07-30T02:06:28+00:00 1 Answers 2 views 0

Answers ( )

    0
    2021-07-30T02:07:40+00:00

    Answer:

    Step-by-step explanation:

    Eq. 1 )   −5x−3y−9=0

    Eq. 2)   4x−18y−54=0

    there are two routes to solve this,   Substitution or  elimination,  I’ll go for the 2nd one because I can see that the y values are a multiple of each other 🙂

        6 *( −5x−3y−9=0 )

    Eq. 3) -30x -18y =54

    subtract Eq. 2 from Eq. 3  🙂

    -30x -18y =54

    -( 4x−18y=54)

    -34x = 0

    so according to the equations then x =0 but,  that’s not really a full answer, so now we should go back and try the other method, substitution,

    then:

    -5x = 9 +3y

    x = – 9/5 + (-3/5)y

    now plug that into Eq. 2

    4( – 9/5 + (-3/5)y ) – 18y = 54

    -36/5 + (-12/5)y -18y = 54

    (-12/5)y – (90/5)y = 54+36/5

    -(102/5)*y =270/5+36/5

    -(102/5)y = 306/5

    y = (-5/102)*(306/5)

    y = -306/102

    y = -3

    then plug in for either equation

    -5x-3( -3) = 9

    -5x + 9 = 9

    -5x = 0

    x = 0

    now we have the full answer

    check it by plugging in both x and y into the 2nd equation

    4(0) – 18(-3) = 54

    54= 54

    this seems good  

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