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AonZ
 2 years ago
Yr11 3unit question help pls!
ABC is a triangle and D is the midpoint of AC. BD=m and angle ADB = theta
(a) show that cos(theta) = 4m^2 + b^2  4c^2 / 4mb
and write an expression for cos(180theta).
(b) show a^2 +c^2 = 2m^2 + 1/2 b^2
I have done part (a) and need help on part (b) pls.
AonZ
 2 years ago
Yr11 3unit question help pls! ABC is a triangle and D is the midpoint of AC. BD=m and angle ADB = theta (a) show that cos(theta) = 4m^2 + b^2  4c^2 / 4mb and write an expression for cos(180theta). (b) show a^2 +c^2 = 2m^2 + 1/2 b^2 I have done part (a) and need help on part (b) pls.

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AonZ
 2 years ago
Best ResponseYou've already chosen the best response.0@jim_thompson5910 @Mertsj help pls

AonZ
 2 years ago
Best ResponseYou've already chosen the best response.0umm im pretty sure ADC is 180. Why wouldnt it be?

Loser66
 2 years ago
Best ResponseYou've already chosen the best response.0since I saw (theta) symbol at ADB and you indicate about ADC is theta

Loser66
 2 years ago
Best ResponseYou've already chosen the best response.0ok, let tag someone who is good at geometry and trig @Mertsj

AonZ
 2 years ago
Best ResponseYou've already chosen the best response.0hmm yes i proved part a but i couldnt get part b. I think you need to do something with part a to get part b

Mertsj
 2 years ago
Best ResponseYou've already chosen the best response.2\[c^2=m^2+(\frac{b}{2})^22m(\frac{b}{2})\cos \theta \]

AonZ
 2 years ago
Best ResponseYou've already chosen the best response.0and cos(180theta) is putting a negative sign infront of that equation

AonZ
 2 years ago
Best ResponseYou've already chosen the best response.0how can we prove part b though?

Mertsj
 2 years ago
Best ResponseYou've already chosen the best response.2From the first part you have an expression for cos (180theta) Get another expression for cos (180theta) using triangle BCD Equate those two expressions for cos(180theta) and solve for a^2+b^2

AonZ
 2 years ago
Best ResponseYou've already chosen the best response.0 4m^2 + b^2  4c^2 / 4mb = 4m^2 + b^2  4a^2 / 4mb right?
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