How do you graph #f(x) = 2x^2 - x - 1 #?

1 Answer
Nallasivam V
Aug 30, 2015

Refer Explanation section

Explanation:

Given -
y = #2x^2- x − 1#

It is a U shaped curve. Since the sign of the#2x^2# is positive, it is concave upwards.
Find the vertex -
x = #(−b)/(2a)= (-(-1))/(2 xx2)= 1/4#
It means when x takes the value #1/4#, the curve turns.
Take a few values on either side of #1/4#. Calculate corresponding y values. Plot the pairs. Join them with the help of a smooth curve

x : y
-3 : 20
-2 : 9
-1 : 2
0 : -1
0.25 : -1.125
1 : 0
2 : 5
3 : 14
4 27
graph{2x^2-x-1 [-10, 10, -5, 5]}

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