# PLEASE…I NEED SOME HELP OVER HERE…:(?

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I have been on this for at least 3 hours I cant figure it out!! I am going insane!!! someone please help me:

1.) solve this system of equations

4x+7y-2z=0

3x-5y+3z=9

3x+6y-z=1

2.)Daniel made an initial deposit of \$85 into a savings account that earns \$2 interest each week. Bridget made a deposit of \$90 into an account that earns \$1 interest each week. If neither Daniel or Bridget make another deposit, after how many weeks will their accounts be equal?

3.)2x – 5y = –12

3x – 4y = 3

Solve the sys. of equations above using the elimination method above

4.) Solve using substitution method:

5x – y = –2

10x – 3y = –7

please i would really appreciate your help!!! i have been on this for hours!!! i just cant get it!

• 1. multiply the 3rd by 3 and add to the 2nd–> new 2nd , multiply the 3rd by 2 and subtract from 1st –> new 1st , multiply new 1st by 6 and add to new 2nd , find y , then x , then z

#2. 5 weeks.. 90 -85 = 5 and 2 -1 = 1 { net gain to \$85 }…5/1 = 5

#3. multiply the 1st by 3/2 and subtract from the 2nd , solve for y , then x

#4. solve the 1st for y , put into the 2nd ..solve for x , then y…you do the work

• 1)

4x +7y – 2z = 0 — (1)

3x – 5y + 3z = 9 — (2)

3x + 6y – z = 1 — (3)

From (3), we have: z = 3x + 6y – 1 — (4)

Substituting (4) into (1), we have:

4x + 7y – 2(3x + 6y – 1) = 0

4x + 7y – 6x – 12y + 2 = 0

-2x – 5y + 2 = 0

2x + 5y – 2 = 0 — (5)

Substituting (4) into (2), we have:

3x – 5y + 3(3x + 6y – 1) = 9

3x – 5y + 9x + 18y – 3 = 9

12x + 13y = 12

13y = 12 – 12x

y = 12/13 – (12/13)x — (6)

Substituting (6) into (5), we have:

2x + 5(12/13 – (12/13)x) – 2 = 0

26x + 5(12 – 12x) – 26 = 0

26x + 60 – 60x – 26 = 0

-34x = -34

x = 1

Substituting x = 1 into (6), we have:

y = 12/13 – (12/13)x

y = 12/13 – 12/13

y = 0

Substituting x = 1 and y = 0 into (4), we have:

z = 3(1) + 6(0) – 1

z = 2

Hence, we have x = 1, y = 0 and z = 2

2)

Let the number of weeks be x

85 + 2x = 90 + x

2x – x = 90 – 85

x = 5

After 5 weeks their accounts will be equal.

3)

2x – 5y = -12 — (1)

3x – 4y = 3 — (2)

From (1), we have:

4(2x – 5y) = 4(-12)

8x – 20y = -48 — (3)

From (2), we have:

5(3x – 4y) = 5(3)

15x – 20y = 15 — (4)

Subtracting (3) from (4), we have:

(15x – 20y) – (8x – 20y) = 15 – (-48)

7x = 63

x = 9

From (1), we have:

2(9) – 5y = -12

18 – 5y = -12

-5y = -30

y = 6

4)

5x – y = -2 — (1)

10x – 3y = -7 — (2)

From (1), we have:

y = 5x + 2 — (3)

Substituting (3) into (2), we have:

10x – 3(5x + 2) = -7

10x – 15x – 6 = -7

-5x = -1

x = 1/5

Substituting x = 1/5 into (3), we have:

y = 5(1/5) + 2

y = 1 + 2

y = 3

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