3x+y=4; 2x−2y=−21
Step: Solve 3x+y=4 for y:
3x+y+−3x=4+−3x (Add -3x to both sides)
y=−3x+4
Step: Substitute−3x+4foryin2x−2y=−21:
2x−2y=−21
2x−2(−3x+4)=−21
8x−8=−21 (Simplify both sides of the equation)
8x−8+8=−21+8 (Add 8 to both sides)
8x=−13
8x
+8
=
−13
8
(Divide both sides by 8)
x=
−13
8
Step: Substitute
−13
8
forxiny=−3x+4:
y=−3x+4
y=−3(
−13
8
)+4
y=
71
8
(Simplify both sides of the equation)
Answer:
x = −13
/8
y = 71
/8
