8 a) y=x² stretched vertically by 8
That means (0,0) stays (0,0), and (1,1) becomes (1,8) and (-1,1) becomes (-1,8)
Answer: y = 8x²
8 b) y=x² compressed vertically by 1/5
Answer: y = (1/5) x²
9.
y = ax² + k through (-1,3) and (3,-13)
That means
3 = a (-1)² + k
-13 = a (3²) + k
Subtracting,
16 = a - 9a = -8a
a = -2
3 = -2 + k
k = 5
y = -2x² + 5
Check:
-2(-1)^2 + 5 = 3, good
-2(3)^2+5 = -18 + 5 = -13, good
Answer: a = -2, k = 5
