Trying to correct DEB maths mock...please help!

Fuascailt

I've my mocks done... I hope this is allowed. Anyone know how to do part (c) (ii) of the circle question (qu 1)? Its driving me nuts:mad:... Thanks..

alan4cult

I'll post solution soon.

alan4cult

Right this part is pretty long

A. So at the start of part c you had two equations:
C1 : x^2 + y^2 + 2(g1)x + 2(f1)y + c1 = 0
C2 : x^2 + y^2 + 2(g2)x + 2(f2)y + c2 = 0

B. Now there are two equations in part 2:
C1 : x^2 + y^2 + 2x - 3y - 4 = 0
C2 : x^2 + y^2 + 2(g)x + 2(f)y + g = 0

Comparing C1 (from A) and C1 (from you get:

2g1 = 2
g1 = 1

2f1 = -3
f1 = -1.5 (the f*****s)

c1 = -4

and Comparing C2 (from A) and C2 (from you get:

2g2 = 2g
g2 = g

2f2 = 2f
f2 = f

c2 = g

Now Radisu(C2) =
sqrt(g^2 + f^2 - g) = 3
g^2 + f^2 -g = 9

Rearranging: f^2 = g - g^2 + 9

From (c) part (i)
2g1g2 + 2f1f2 = c1 + c2
2(1)(g) + 2(-1.5)(f) = -4 + g
2g - 3f = - 4 + g
3f = 4+g
f = (4+g)/3
f^2 = (16 + 8g + g^2)/9

Now f^2 = f^2

g - g^2 + 9 = (16 + 8g + g^2)/9
9g - 9g^2 + 81 = 16 + 8g + g^2

10g^2 - g - 65 = 0

Now use quadratic formula:

g = [1 +- sqrt(1 + 2600)]/2(10)
g = [1 +- 51]/20

g = 52/20 = 2.6 or g = -50/20 = -2.5

Then f = [4+g]/3
f = [4+2.6]/3 = 2.2
f = [4-2.5]/3 = 0.5

Look I made it very long and it may be wrong (open to correction)

Alan

Fuascailt

Thanks a million! Yeah, i think thats right. I just realised that i didn't notice they changed the c2 to a g...Grrrrrrr... so i had three unknowns:rolleyes: some ones going to be reading questions very carefully for the real thing!