I’m on my phone on a lunch break but as a starting point:

From the information given, you know that when x = 2, y = 3. You also know that when x = 3, y = 11. EDIT: no you don’t

You can put in those values and try to solve by trial and error, or by using simultaneous equations.

(edited 4 years ago)

Reply 4

Chinemerem1

11

Original post by asifmahmoud

A curve has equation
Y=x^3+px^2+qx-45
The curve passes through point R (2,3)
The gradient of the curve is 8
Find p and q

Dont you differentiate, then substitute x and make dy/dx=8. That makes one equation.
Then substitute coordinates into f(x) to get other equation, then solve simultaneously

(edited 4 years ago)

Reply 5

Chinemerem1

11

I got the same answer as you.

Original post by asifmahmoud

I got p= -12 and q=44 but not sure

Reply 6

username1586817

14

EDIT: I WAS WRONG DONT DO THIS

3 = 2^3 + p(2^2) + q(2) - 45
= 8 + 4p + 2q - 45
= 4p + 2q - 37

11 = 3^3 + p(3^2) + q(3) - 45
= 27 + 9p + 3q - 45
= 9p + 3q - 18

Therefore

4p + 2q = 40
9p + 3q = 29

(edited 4 years ago)

Reply 7

Chinemerem1

11

Original post by MyMaths&chill

I’m on my phone on a lunch break but as a starting point:

From the information given, you know that when x = 2, y = 3. You also know that when x = 3, y = 11.

You can put in those values and try to solve by trial and error, or by using simultaneous equations.

How do you know when x=3, y=11

Reply 8

That 36 Boy

OP

15

If so, when i solve the two equations simultaneously, i get p= -31/3 and q = 122/3 which doesn't seem to be the answer. I also don't know what's wrong with my answer either

Original post by MyMaths&chill

I’m on my phone on a lunch break but as a starting point:

From the information given, you know that when x = 2, y = 3. You also know that when x = 3, y = 11.

You can put in those values and try to solve by trial and error, or by using simultaneous equations.

Reply 9

username1586817

14

Oh **** yeah I did this wrong ignore what I said lol

Don’t mix lunch and maths, it doesn’t work

Original post by Chinemerem1

How do you know when x=3, y=11

Reply 10

That 36 Boy

OP

15

If you calculate the gradient from those two points (2,3) and (3,11) you get gradient to be 8

Original post by Chinemerem1

How do you know when x=3, y=11

Reply 11

Chinemerem1

11

Original post by asifmahmoud

If you calculate the gradient from those two points (2,3) and (3,11) you get gradient to be 8

That's for straight lines, this is a curve

Reply 12

username1586817

14

Yeah this is the correct approach.

Oops

Original post by Chinemerem1

Dont you differentiate, then substitute x and make dy/dx=8. That makes one equation.
Then substitute coordinates into f(x) to get other equation, then solve simultaneously