How do you solve y=sqrt xy=x and y=x-6y=x6 using substitution?

1 Answer
Sep 29, 2016

When x = 9 , y = 2 " or " 3"x=9,y=2 or 3
When x = 4 , y = 3 " or " -2 x=4,y=3 or 2

Explanation:

You can solve the equations by equating the y's and then substituting for each y.

color(red)(y = sqrtx) color(white)(xxxx)and " "color(blue)(y = x-6)y=x××and y=x6

color(white)(xxxxxxxxx) color(red)(y) = color(blue)(y)××××xy=y

Therefore..color(red)( sqrtx) = color(blue)(x-6)" "larrx=x6 only x terms

(sqrtx)^2 = (x-6)^2 " "larr(x)2=(x6)2 square both sides.

x = x^2 -12x +36" "larrx=x212x+36 make the quadratic = 0

x^2 -13x + 36 = 0" "larrx213x+36=0 factorize

Find factors of 36 which ADD to 13. Signs are both negative.

(x-9)(x-4) = 0(x9)(x4)=0

If x-9 = 0 rarr x = 9" "x9=0x=9 OR If " "x-4 =0 rarr x = 4 x4=0x=4
Now find y.
color(red)(y = sqrtx) color(white)(xxxx)and " "color(blue)(y = x-6)y=x××and y=x6

y = sqrt 9 = 3" "larry=9=3 only the principal square root was indicated
y=sqrt4 = 2y=4=2
y = x-6 rarr y = 9-6 = 3y=x6y=96=3
y = x-6 rarr y = 4-6 = -2y=x6y=46=2