Question

4x – y = 7 3y – 12x = –21

Answer 1

Step: Solve
4
x
−
y
=
7
for y:
4
x
−
y
=
7
4
x
−
y
+
−
4
x
=
7
+
−
4
x
(Add -4x to both sides)
−
y
=
−
4
x
+
7
−
y
−
1
=
−
4
x
+
7
−
1
(Divide both sides by -1)
y
=
4
x
−
7

Step: Substitute
4
x
−
7
for
y
in
−
12
x
+
3
y
=
−
21
:
−
12
x
+
3
y
=
−
21
−
12
x
+
3
(
4
x
−
7
)
=
−
21
−
21
=
−
21
(Simplify both sides of the equation)
−
21
+
21
=
−
21
+
21
(Add 21 to both sides)
0
=
0

Answer 2

y=4x-7 3(4x-7)-21x=-21 12x-21-12x=-21 -21=-21

Explanation: