mathematics function F.4 (40)

The direction of opening is determined by

the sign of the coefficent of x^2.

+ve means opening upwards;
-ve means opening downwards.


y - intercept always EQUAL to the constant term of the function.


function:
y = -x^2 - x+1

(1)
the coefficent of x^2 = -1
so the sign is -ve

the direction of opening hence is downwards.

(2)
constant term is +1
so the y - intercept is +1


function:
y = -3+x+2x^2

(3)
the coefficent of x^2 = +2
so the sign is +ve

the direction of opening hence is upwards.

(4)
constant term is -3
so the y - intercept is -3

(1)open downward,y intercept:1
(2)open upward,y-intercepy:-3