# Help!! On Substitution and Elimantion method! PLEASEE!?

+1 vote

My problem is 9x+4y=12
x+4y=18

9x+4y=12-------------(1)

x+4y=18--------------(2)

subtract 4y is the  each  side

x =18 -4y

substution  the x value eqution (1)

9(18 -4y) +4y =12

162 - 36y +4y =12

-32y =12 -162

32 y=150

bothside divide by  32

y=150 /32

=75 /16

substution  the y value eqution (2)

x+4(75 /16) =18

x +75/4 =18

subtract 75/4 is the  each  side

x =18 - 75/4

x = (72 -75)/4

x = -3/4

the values are (x , y) =( -3/4 ,75/4)

# Elimantion method

9x+4y=12-------------(1)

(-)   x+4y=18--------------(2)

---------------------------------------

8x  = -6

x  = -6/8

x = -3/4

substution  the x value eqution (2)

-3/4 +4y = 18

addition the  -3/4 is the  each  side

4y = 18 +3/4

4y =(72 +3 )/4

y =75/16

the values are (x , y) =( -3/4 ,75/16)

9x+4y=12-------------(1)

x+4y=18--------------(2)

subtract 4y is the  each  side

x =18 -4y

substution  the x value eqution (1)

9(18 -4y) +4y =12

162 - 36y +4y =12

-32y =12 -162

32 y=150

bothside divide by  32

y=150 /32

=75 /16

substution  the y value eqution (2)

x+4(75 /16) =18

x +75/4 =18

subtract 75/4 is the  each  side

x =18 - 75/4

x = (72 -75)/4

x = -3/4

the values are (x , y) =( -3/4 ,75/16)

9x+4y=12  --------------(1)
x+4y=18  ------------------(2)

(1)-(2)⇒   9x+4y=12

(-)        x+4y=18

------------------------

9x-x+4y-4y=12-18

8x=-6

dividedby 8 each side

(8x/8)=(-6/8)

x=(-2*3)/(2*4)

x=-3/4

there fore x= -3/4

x value substuting in equation (2)

(2)⇒x+4y=18

(-3/4)+4y=18

(-3/4)+4y+3/4=18+3/4

4y=(72+3)/4                           LCM 1,4 is 4

4y=75/4

dividedby 4 each side

4y/4=(75/4)/4

y=75/16

there fore x= -3/4 , y=75/16