SOLUTION: solve using substitution method (a)y=x-7 (b) 3x+7y=5 3x-y=-1 x+4y=5 solve using elimination 3x+2y=19 x-2y=3

Algebra ->  Coordinate Systems and Linear Equations  -> Lessons -> SOLUTION: solve using substitution method (a)y=x-7 (b) 3x+7y=5 3x-y=-1 x+4y=5 solve using elimination 3x+2y=19 x-2y=3      Log On


   

Question 417848: solve using substitution method
(a)y=x-7 (b) 3x+7y=5
3x-y=-1 x+4y=5
solve using elimination
3x+2y=19
x-2y=3
Answer by MathLover1(20850) About Me  (Show Source):
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substitution method
(a)
y=x-7 .....1..substitute y in 2

3x-y=-1...2
3x-%28x-7%29=-1
3x-x%2B7=-1
2x=-1-7
2x=-8%7D%7D%0D%0A%0D%0A%7B%7B%7Bx=-4%7D%7D...now+find+%7B%7B%7Bx
y=-4-7
y=-11

check:
-11=-4-7 .....1
-11=-11

(b)
3x%2B7y=5.....1
+x%2B4y=5.....2.solve for x
+x=-4y%2B5.plug in 1
3%28-4y%2B5%29%2B7y=5.....1.solve for y
-12y%2B15%2B7y=5
-5y=5-15

-5y=-10
y=2............find x
+x=-4%2A2%2B5
+x=-8%2B5
+x=-3

check:
3%28-3%29%2B7%2A2=5.....1
-9%2B14=5
5=5

solve using elimination
3x%2B2y=19
x-2y=3.....add both
--------------------
3x%2Bx%2B2y-2y=19%2B3

3x%2Bx%2Bcross%282y%29-cross%282y%29=19%2B3

4x=22
x=22%2F4
x=5.5......find y

3%2A5.5%2B2y=19

16.5%2B2y=19
2y=19-16.5
2y=2.5
y=2.5%2F2
y=1.25


check:
3%2A5.5%2B2%2A1.25=19
16.5%2B2.5=19
19=19