Question

Solve the system by substitution.

y = 2x


3x + 2y = 21

Answer 1

y=2x;3x+2y=21

Solve y=2x for y

Substitute (2x) for y in 3x+2y=21

3x+2y=21

3x+22x=21

7x=21 (Simplify)

7x / 7 = 21 / 7(Divide both sides by 7)

x=3

Substitute (3) for x in y=2x:

y=2x

y=(2)(3)

y=6 (Simplified)

y=6 and x=3

Answer 2

`\left \{ {{y=2x} \atop {3x+2y=21}} \right \longrightarrow \left \{ {{y=2x} \atop {3x+2\cdot2x=21}} \right. \longrightarrow \left \{ {{y=2x} \atop {7x=21}} \right.\longrightarrow \left \{ {{y=2x} \atop \boxed{{x=3}}} \right. \\\\y=2x\longrightarrow y=2\cdot3\longrightarrow \boxed{y=6}`