Question

Find the solution to the system by the substitution methond.
y=4x-4
y=5x

a.(1,0)
b.(-4,-20)
c.(4,0)
d.(-3,-15)

(Im confused !!!please explain to me how get the answer)!

Answer 1

y = 5 x Divide both sides by 5

y / 5 = x

x = y / 5


y = 4 x - 4

y = 4 * ( y / 5 ) - 4

y = 4 y / 5 - 4 Subtract 4 y / 5 to both sides

y - 4 y / 5 = 4 y / 5 - 4 - 4 y / 5

y - 4 y / 5 = - 4

5 y / 5 - 4 y / 5 = - 4

y / 5 = - 4 Multiply both sides by 5

y = - 20


x = y / 5

x = - 20 / 5

x = - 4


The solutions are:

x = - 4 and y = - 20

Answer b

Answer 2

Since it asked for substitution, why not just sub the 2nd into the 1st

5x = 4x - 4
x = -4
now back into the 2nd:
y = 5x= 5(-4) = -20

so the intersection point is (-4,-20)