Answer:
The vertex is (2,1)
Step-by-step explanation:
ƒ(x) = –x^2 + 4x – 3
Factor out the negative
= -(x^2 -4x+3)
Factor
What 2 numbers multiply to +3 and add to -4
-3*-1 = 3
-3+-1 = -4
f(x) = -( x-3)(x-1)
Find the zeros
0 = -( x-3)(x-1)
0 = x-3 0 = x-1
x=3 x=1
The x value of the vertex is 1/2 way between the two zeros
(3+1)/2 = 4/2 =2
To find the y value, substitute x=2 in
f(2) = -( 2-3)(2-1)
=-(-1)(1) = 1
The vertex is (2,1)
-x - y = 8
2x - y = -1
Ok, we are going to solve this in 2 parts. First we have to solve for one of the variables in one of the equation in terms of the other variable. I like to take the easiest equation first and try to avoid fractions, so let's use the first equation and solve for x.
-x - y = 8 add y to each side
-x = 8 + y divide by -1
x = -8 - y
So now we have a value for x in terms of y that we can use to substitute into the other equation. In the other equation we are going to put -8 - y in place of the x.
2x - y = -1
2(-8 - y) - y = -1 multiply the 2 through the parentheses
-16 - 2y - y = -1 combine like terms
-16 - 3y = -1 add 16 to both sides
-3y = 15 divide each side by -3
y = -5
Now we have a value for y. We need to plug it into either of the original equations then solve for x. I usually choose the most simple equation.
-x - y = 8
-x - (-5) = 8 multiply -1 through the parentheses
-x + 5 = 8 subtract 5 from each side
-x = 3 divide each side by -1
x = -3
So our solution set is
(-3, -5)
That is the point on the grid where the 2 equations are equal, so that is the place where they intersect.
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