9 divided by 72 = 0.125
0.125 is the weight of one book
0.125 times 80 = 10kg.
So 80 books weight 10kg.
72 divided by 9 = 8 books make up 1 kg.
8 times 6 =48

4 0

3 years ago

What is the vertex of a parabola having the equation y = –2(x – 5)2 + 7? Which direction does the parabola open?

Vika [28.1K]

$y = -2(x-5)^2 + 7$

That's vertex form for a parabola $y=a(x-p)^2+q$ and we read off vertex (p,q) as

Answer: Vertex (5,7)

The negative a tells us this is a downward opening parabola (upside down from the usual $y=x^2$ . I remember CUP - Concave Up Positive; here a is negative so not a cup, instead concave down. The same rule applies to second derivatives in calculus so memorize it now and use it later.