mvictor wrote:
is there a faster way to solve it???
my approach
we have -x^2, so parabola is downwards
when x=0, y=0, so (0;0) is a point on the parabola.
another point of intersection with x axis is x=6.
now..
x=5; y=5
x=4; y=8
x=3; y=9
x=2; y=8
x=1; y=5
everything below is inside the parabola
1. 1;4 - is inside, because 1;5 is on the parabola.
2. 3;6 - is inside, because 3;9 is on the parabola.
3. 5;4 - is inside, because 5;5 is on the parabola.
E
Yes, you know that since co-efficient of x^2 is negative, the parabola will be downward facing. So the parabola and the x axis will enclose some points. We don't even need to draw out the parabola.
Just put the relevant points in y = x(6 - x)
x = 1, y = 5 lies on the parabola. So (1, 4) will lie below it. Hence, it will be enclosed by the parabola and x axis.
x = 3, y = 9 lies on the parabola. So (3, 6) will lie below it. Hence, it will be enclosed by the parabola and x axis.
x = 5, y = 5 lies on the parabola. So (5, 4) will lie below it. Hence, it will be enclosed by the parabola and x axis.
Answer (E)
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69% (02:40) correct 
