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AonZ
Group Title
Help please :) Yr11 3 unit question on trig
In triangle ABC, acosA = bcosB. Prove using the cosine rule, that the triangle is either isosceles or rightangled
 one year ago
 one year ago
AonZ Group Title
Help please :) Yr11 3 unit question on trig In triangle ABC, acosA = bcosB. Prove using the cosine rule, that the triangle is either isosceles or rightangled
 one year ago
 one year ago

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ajprincess Group TitleBest ResponseYou've already chosen the best response.2
Do u knw cos rule?
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
good:) so vat is cosA?
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
b^2 + c^2  a^2 / 2bc
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
a^2 +c^2  b^2 / 2ac
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
Nw if u r to prove that the triangle is isoscles u need to show that a=b or b=c or a=c. if u r to show it is a right angled triangle u should show pythagoras theorem is valid. \[a\cos A=b\cos B\] \[a* \frac{ b^2+c^2a^2 }{ 2bc}=b*\frac{ a^2+c^2b^2 }{ 2ac }\] vat do u get when u simplify this? @AonZ
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
2c^3 a^2  2a^4 c  2c^3 b^2 + 2b^4 c = 0
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
u can factor out 2c.
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
2c ( b^4  c^2 b^2 + a^2 c^2  a^4) = 0 this right so far?
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
yup:) good:) nw divide by 2c both sides.
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
ok done that. btw im writing it down
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
u will get this. b^4  c^2 b^2 + a^2 c^2  a^4=0 try to factorise this.
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
(b^2  a^2)(b^2 +a^2 c^2)
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
(b+a)(ba)(b^2+a^2  c^2)
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
(b+a)(ba)(b^2+a^2  c^2)=0 Divide by (b+a)(ba) both sides. vat do u get?
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
b^2 +a^2  c^2 = 0
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
you can tell its right angle by looking at this.. but how do you tell if its isosceles?
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
u r nt asked to prove both right? either one of that?
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
oh i guess :)
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
i still think it means to prove that the triangle must be right or isoscles but it cant be scalene
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
but can we show it isoscles anyways?
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
let me think. hav to go nw. will be back in 15 mnts
 one year ago

gohangoku58 Group TitleBest ResponseYou've already chosen the best response.1
(b+a)(ba)(b^2+a^2  c^2) =0 gives (b+a)=0 OR (ba)= 0 OR (b^2+a^2  c^2)=0 so, ba = 0 >a=b>isosceles (b^2+a^2  c^2)=0 >right as you already know.
 one year ago

AonZ Group TitleBest ResponseYou've already chosen the best response.0
ohh xDDDD THANKS!! Shame i can only give medal to 1 person :(
 one year ago

gohangoku58 Group TitleBest ResponseYou've already chosen the best response.1
hey, i am not here for medals ;)
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
Welcome:) you can give it to @gohangoku58
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
cos he/she deserves it most:)
 one year ago

gohangoku58 Group TitleBest ResponseYou've already chosen the best response.1
:O You made him solve the whole thing and i deserve it!??
 one year ago

ajprincess Group TitleBest ResponseYou've already chosen the best response.2
yup:) it was u who pointed out the isoscles one:)
 one year ago
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