The Student Room Group
Reply 1
Area of a triangle is (1/2)|ABxAC|
Try using that, and see how you do...
Reply 2
See attachment.
Reply 3
Gaz031
See attachment.


Cheers gaz, i was being retarded and didn't square the area when i squared the determinant. careless ay, blimey.
thanks again
Reply 4
Here's another:

solve 5z^4 - 11z^3 + 16z^2 -11z + 5 = 0
using z^n + z^(-n) = 2cos(n&#952:wink:

I've got as far as 5(z^2 + z^-2) - 11(z + z^-1) +16 = 0

so 10cos2θ - 22cosθ + 16 = 0

do you just solve that or what?????
Reply 5
solve for cos@.
Now substitute for cos@ into z + z^-1 = 2cos @
create a quadratic in z.
solve for z.
Reply 6
Fermat
solve for cos@.
Now substitute for cos@ into z + z^-1 = 2cos @
create a quadratic in z.
solve for z.


Makes sense! Cheers guv
Reply 7
Solve the quadratic equation in cosθ, noting that cos2θ = 2cos^2θ + 1.
Reply 8
JamesF
Solve the quadratic equation in cosθ, noting that cos2θ = 2cos^2θ + 1.


Sorry, I forgot to say it says write the answer in the form a + ib.

so i guess i write z = a + ib and solve the quadratic in that form to get
z = 1/2 + [root(3)/2]i
z = 3/5 + (4/5)i

think that's right, correct me if I'm wrong
Reply 9
Sorry, but ...

cos @ = 1/2 or cos@ = 3/5.

Now substitute for cos@ into z + 1/z = 2cos @
You should get two values of z ( = a + ib) for each value of cos@ - four values in all.
It is a quartic eqn after all, so four roots.

Edit:
what you have is correct - just add in the +/- signs.

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