Question

a parabola whose axis is parallel to the y axis passess through the points {1,1), (2.2) and (-1,5). Find the equation of the parabola

Answer 1

let the equation have the form
y = ax^2 + bx + c
for (1,1) --> 1 = a + b + c
for (2,2) --> 2 = 4a + 2b + c
for (-1,5) --? 5 = a - b + c

subtract #1 - #3: 2b = -4 , b = -2

subtract #2 - #1: 3a + b = 1
sub in b = -2
3a - 2 = 1
3a = 3
a = 1
sub into the first:
1 - 2 + c = 1
c = 2

your equation is:
y = x^2 - 2x + 2