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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.
 11 months ago
 11 months 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.
 11 months ago
 11 months ago

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AonZBest ResponseYou've already chosen the best response.0
@jim_thompson5910 @Mertsj help pls
 11 months ago

AonZBest ResponseYou've already chosen the best response.0
umm im pretty sure ADC is 180. Why wouldnt it be?
 11 months ago

Loser66Best ResponseYou've already chosen the best response.0
since I saw (theta) symbol at ADB and you indicate about ADC is theta
 11 months ago

AonZBest ResponseYou've already chosen the best response.0
im sorry ADB is theta :P
 11 months ago

Loser66Best ResponseYou've already chosen the best response.0
ok, let tag someone who is good at geometry and trig @Mertsj
 11 months ago

AonZBest ResponseYou've already chosen the best response.0
hmm 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
 11 months ago

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

AonZBest ResponseYou've already chosen the best response.0
ok yea i proved that part
 11 months ago

AonZBest ResponseYou've already chosen the best response.0
and cos(180theta) is putting a negative sign infront of that equation
 11 months ago

AonZBest ResponseYou've already chosen the best response.0
how can we prove part b though?
 11 months ago

MertsjBest ResponseYou've already chosen the best response.2
From 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
 11 months ago

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

AonZBest ResponseYou've already chosen the best response.0
ok i solved it thank you
 11 months ago
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