SOLUTION: Solve and check the following systems by elimination. Show steps. Check both equations. 4. (3x � 4y = -30) (7x + 4y = 10 ) 5. (x � 4y = 29 ) (3x + 2y = -11)

Click here to see ALL problems on Graphs

Question 376676: Solve and check the following systems by elimination. Show steps. Check both equations.
4.
(3x � 4y = -30)
(7x + 4y = 10 )

5.
(x � 4y = 29 )
(3x + 2y = -11)

6.
(4x + 3y = -4)
(3x � 7y = 34)

Answer by sophxmai(62) (Show Source):
You can put this solution on YOUR website!
#4
Equation 1:(3x � 4y = -30)
Equation 2:(7x + 4y = 10)

Add the 2 equations, the y should cancel out.
3x � 4y = -30
7x + 4y = 10
10x + 0y = -20 <-- this simplifies to 10x = -20

From here, solve for x.
10x = -20

x = -2

Now substitute x with x = -2 in one of the 2 equations.
Equation 1:(3x � 4y = -30)
3x � 4y = -30
3(-2) � 4y = -30
-6 - 4y = -30
-4y = -24
y = 6

#5
Equation 1:(x � 4y = 29)
Equation 2:(3x + 2y = -11)

Multiply equation 1 by 3 so that the coefficient of x in both equations are the same.
x � 4y = 29
3x - 12y = 87 <-- Let this be equation 3.

Now subtract equation 3 from equation 2.
3x + 2y = -11
3x - 12y = 87
0x + 14y = -98 <-- This simplifies to 14y = -98

Solve for y.
14y = -98

y = -7

Substitute y for y = -7 in one of the 3 equations.
Equation 1:(x � 4y = 29)
x � 4y = 29
x � 4(-7) = 29
x + 28 = 29
x = 1

Now try to do #6 by yourself using this method. If you need help with #6 after you've tried it, just message me.