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AonZ
 3 years ago
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
AonZ
 3 years ago
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

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ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2good:) so vat is cosA?

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2Nw 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

AonZ
 3 years ago
Best ResponseYou've already chosen the best response.02c^3 a^2  2a^4 c  2c^3 b^2 + 2b^4 c = 0

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2u can factor out 2c.

AonZ
 3 years ago
Best ResponseYou've already chosen the best response.02c ( b^4  c^2 b^2 + a^2 c^2  a^4) = 0 this right so far?

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2yup:) good:) nw divide by 2c both sides.

AonZ
 3 years ago
Best ResponseYou've already chosen the best response.0ok done that. btw im writing it down

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2u will get this. b^4  c^2 b^2 + a^2 c^2  a^4=0 try to factorise this.

AonZ
 3 years ago
Best ResponseYou've already chosen the best response.0(b^2  a^2)(b^2 +a^2 c^2)

ajprincess
 3 years ago
Best 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?

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

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

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

AonZ
 3 years ago
Best ResponseYou've already chosen the best response.0but can we show it isoscles anyways?

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2let me think. hav to go nw. will be back in 15 mnts

anonymous
 3 years ago
Best ResponseYou've already chosen the best response.0(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.

AonZ
 3 years ago
Best ResponseYou've already chosen the best response.0ohh xDDDD THANKS!! Shame i can only give medal to 1 person :(

anonymous
 3 years ago
Best ResponseYou've already chosen the best response.0hey, i am not here for medals ;)

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2Welcome:) you can give it to @gohangoku58

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2cos he/she deserves it most:)

anonymous
 3 years ago
Best ResponseYou've already chosen the best response.0:O You made him solve the whole thing and i deserve it!??

ajprincess
 3 years ago
Best ResponseYou've already chosen the best response.2yup:) it was u who pointed out the isoscles one:)
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