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Question Number 216245 by Tawa11 last updated on 01/Feb/25

Commented by Tawa11 last updated on 01/Feb/25

I can use cosine rule.  But I want to see if there is  better approach.

Icanusecosinerule.ButIwanttoseeifthereisbetterapproach.

Commented by Tawa11 last updated on 01/Feb/25

I got   x  +  y  =  50.  But to proceed gives me  maths error.

Igotx+y=50.Buttoproceedgivesmemathserror.

Commented by mr W last updated on 02/Feb/25

we can find x=30° purely  geometrically without using sine or   cosine rules.  show your solution using cosine rule.

wecanfindx=30°purelygeometricallywithoutusingsineorcosinerules.showyoursolutionusingcosinerule.

Commented by Tawa11 last updated on 01/Feb/25

Commented by Tawa11 last updated on 01/Feb/25

I represent those equal length as 1.  I leant that from you sir.         BD  =  (√(2  −  2cos40))  Then, I found BC.         BC  =  1^2   +  ((√(2  −  2cos40)))^2   −  2(1)(2  −  2cos40)cos130         BC  =  3  −  2cos40  −  2(2  −  2cos40)cos130  So,      ((sin x)/1)  =  ((sin130)/(3  −  2cos40  −  2(2  −  2cos40)cos130))  So, I am getting   x  approximately   32   now.

Irepresentthoseequallengthas1.Ileantthatfromyousir.BD=22cos40Then,IfoundBC.BC=12+(22cos40)22(1)(22cos40)cos130BC=32cos402(22cos40)cos130So,sinx1=sin13032cos402(22cos40)cos130So,Iamgettingxapproximately32now.

Commented by mr W last updated on 02/Feb/25

wrong!         BC^2   =  1^2   +  ((√(2  −  2cos40)))^2   −  2(1)(√(2  −  2cos40)) cos130

wrong!BC2=12+(22cos40)22(1)22cos40cos130

Commented by Tawa11 last updated on 02/Feb/25

Ohhh.  How I did not see that?  Thank you sir, I really appreciate.

Ohhh.HowIdidnotseethat?Thankyousir,Ireallyappreciate.

Answered by mr W last updated on 01/Feb/25

Commented by mr W last updated on 02/Feb/25

blue numbers indicate the steps  x=70−40=30°

bluenumbersindicatethestepsx=7040=30°

Commented by Tawa11 last updated on 02/Feb/25

Thanks sir.  I appreciate.

Thankssir.Iappreciate.

Commented by ArshadS last updated on 02/Feb/25

Sir I  coudn′t understand step  5. How is it  40 ?

SirIcoudntunderstandstep5.Howisit40?

Commented by mr W last updated on 02/Feb/25

∠AED=60+40=100°  EA=ED   ⇒∠EAD=∠EDA=((180−100)/2)=40°

AED=60+40=100°EA=EDEAD=EDA=1801002=40°

Commented by ArshadS last updated on 03/Feb/25

Thanks Sir! I understood now.

ThanksSir!Iunderstoodnow.

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