All Junior Cert Mathematics posts
• #### Functions problem hamzamughees

Hey Guys,

If you look at the 2014 junior cert higher level maths paper 1 question 10, part a tells us two functions, f(x) and g(x), and asks us to identify from two given graphs, which one represents one of these given functions, i am having difficulties with this question... Any help please?

1. #### LCC1

Sub in values into the line function, then look at graph and then you will be easily able to identify the line

eg f(2) - sub in 2 into the line eg F(X) 2(x) +3. Then 2(2) + 3 = 7 Point for graph line is then (2 7)

check where this is graphed, then this is f(x) line

2. #### hamzamughees

thanks a million LCC1.

3. #### Dazzla16

There is an easy way to answer that question. In the function f(x) the coefficient of x^2 is positive. That means it must take up the shape of a 'happy face'. In the function g(x) the coefficient of x^2 is negative. That means it must take up the shape of a 'sad face'.

4. #### Dazzla16

You can also do this: input 0 into both equations.

f(0) = (0)^2 + 2(0) - 3 = -3 (That means this function touches the point (0,-3))

g(0) = -(0)^2 - 2(0) + 3 = 3 (That means this function touches the point (0,3))

That means f(x) is matched with the first graph and g(x) is matched with the second graph.

By the way, @LCC1 I would like to correct a slight mistake you made.

If you input 2 into the function f(x), you get f(2) = (2)^2 + 2(2) - 3 = 5 (That means this function touches the point (2,5)). Other than that, you've got the right idea.

5. #### hamzamughees

thanks a million Dazzla16

6. #### Dazzla16

@LCC1 I'm sorry. I thought you were referring to the actual exam question. You actually made no mistakes with your example, it's just the example you gave was similar to the exam question hamzamughees mentioned. That's why I thought you made a mistake.