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# Help with maths past paper questions watch

1. [From MEI Jun 2011, C1]
12.) Fig, 12. Shows the graph of y = 4 / x^2.

(i) In the copy of Fig, 12. draw accurately the line y = 2x + 5 and hence find graphically the three roots of the equation 4 / x^2 = 2x + 5. (3 marks)

(ii) Show that the equation you have solved in part (i) may be written as 2x^3 + 5x^2 - 4 = 0. Verify that x = -2 is a root of this equation and hence find, in exact form the other two roots. (6 marks)

(iii) By drawing a suitable line on the copy of Fig, 12. find the number of real roots of the equation x^3 + 2x^2 - 4 = 0. (3 marks)

I can't work out 12 part iii.

2. (Original post by 12laus)
[From MEI Jun 2011, C1]
12.) Fig, 12. Shows the graph of y = 4 / x^2.

(i) In the copy of Fig, 12. draw accurately the line y = 2x + 5 and hence find graphically the three roots of the equation 4 / x^2 = 2x + 5. (3 marks)

(ii) Show that the equation you have solved in part (i) may be written as 2x^3 + 5x^2 - 4 = 0. Verify that x = -2 is a root of this equation and hence find, in exact form the other two roots. (6 marks)

(iii) By drawing a suitable line on the copy of Fig, 12. find the number of real roots of the equation x^3 + 2x^2 - 4 = 0. (3 marks)

I can't work out 12 part iii.

Can you draw the line y = x + 2?
3. (Original post by Mr M)
...
Part (iii)
4. (Original post by ghostwalker)
Part (iii)
Do you prefer y = x + 2 ?

5. To explain you want to turn into something of the form
6. (Original post by Mr M)
To explain you want to turn into something of the form
Thanks, I had looked at the mark scheme and could not find out where to get y=x+2 from. So thanks for that!
7. (Original post by 12laus)
Thanks, I had looked at the mark scheme and could not find out where to get y=x+2 from. So thanks for that!
You are welcome.

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