nce the line of symmetry is x = 2, the x coordinate of the vertex must = 2
And the x coordinate of the vertex is given by : -b/2a.......so we have that
2 = -b/[2a] → -4a = b
And we have these equations
1 = a(1)^2 - 4a(1) + c → 1 = -3a + c (1)
-1 = a(4)^2 - 4a(4) + c → -1 = c (2)
Subbing (2) into (1) we have that 1 = -3a - 1 → 2 = -3a → a = -2/3
Which means that b = -4(-2/3) = 8/3
So....the equation of the quadratic is :
y = (-2/3)x^2 + (8/3)x - 1
And we know that
0 = (-2/3)(√n +2)^2 + (8/3)(√n + 2) - 1 let √n + 2 = m.......and we have that
0 = (-2/3)m^2 + (8/3)m - 1 multiply both sides by 3
0 = -2m^2 + 8m - 3 complete the square on m
3 - 8 = -2 (m^2 - 4m + 4)
-5 = -2 (m - 2)^2
5/2 = (m - 2)^2 take pos/neg square roots
±√[5/2] = m - 2
±√[5/2] + 2 = m back-substituting, we have
±√[5/2] + 2 = √n + 2 and since we want the larger root
√[5/2] = √n
n = 5/2 = 2.5
Here's the graph : https://www.desmos.com/calculator/102umpw19h
The larger root = ( √2.5 + 2 , 0 ) ≈ ( 3.581, 0 )