SOLUTION: solve by substitution method: x + 3y = -8,4x - 3y = 23 solve by substitution: x - 2y = -3 and y = 2x - 3 find f(-2) given that f(s) = -x^2 - 4x + 23

Algebra ->  Expressions-with-variables -> SOLUTION: solve by substitution method: x + 3y = -8,4x - 3y = 23 solve by substitution: x - 2y = -3 and y = 2x - 3 find f(-2) given that f(s) = -x^2 - 4x + 23      Log On


   

Question 173659: solve by substitution method: x + 3y = -8,4x - 3y = 23
solve by substitution: x - 2y = -3 and y = 2x - 3
find f(-2) given that f(s) = -x^2 - 4x + 23
Answer by jojo14344(1513) About Me  (Show Source):
You can put this solution on YOUR website!
solve by substitution method: x+%2B+3y+=+-8 EQN 1,
4x+-+3y+=+23, EQN 2
In EQN 1 we get, x=-8-3y, EQN 3, subst in EQN 2:
4%28-8-3y%29-3y=23
-32-12y-3y=23
-15y=23%2B32=55, divide both terms by -15
highlight%28y=-3.67%29, subst in EQN 3
x=-8-3%28-3.67%29=-8%2B11
highlight%28x=3%29
Check via EQn 1:
3%2B3%28-3.67%29=-8
3-11.01=8
-8.01=-8 close enough
.
solve by substitution: x+-+2y+=+-3, EQN 4 and y+=+2x+-+3, EQN 5
In EQN 4:
x=-3%2B2y, EQN 6, subst in EQN 5:
y=2%28highlight%28-3%2B2y%29%29-3
y=-6%2B4y-3
4y-y=6%2B3
3y=9----->cross%283%29y%2Fcross%283%29=cross%289%293%2Fcross%283%29
highlight%28y=3%29, subts in EQN 6
x=-3%2B2%283%29=-3%2B6
highlight%28x=3%29
Check via EQN 5:
3=2%283%29-3
3=6-3
3=3 good
.
find f(-2) given that f(s) = -x^2 - 4x + 23
f%28s%29=-%28-2%29%5E2-4%28-2%29%2B23
f%28s%29=-4%2B8%2B23=highlight%2827%29
Thank you,
Jojo