IIT JEE , AIEEE Forum - Mathematics , Trignometry

m.viddya

Q.Out of all the triangles with a=5 and A=30^o if the area

of triangle ABC is maximum then angle B=?

1.30^o

2.75^o

3.150^o

4.90

eistien

hey by sine rule we know that b=10 sinB c=10sinC

as a/sinA=5/(1/2)=10

now area of triangle is (1/2)bcsinA

which is 25 sinB sinC

but C=5pie/6-B

substitute for C in the above equation and differentiate wrt to B and solve for B!!!

eistien

Answer is C 150 is the right answer!!!!the third option!!!

sandeepramesh

so mr einstein do you mean to say that A = 30, B = 150 and then C = 0??? Thats the new wonder triangle you have discovered?

hash_include

ha ha.. nice one einstein :D

but by intuition, me thinks the answer should be an isoceles triangle..
so answer is 75 degrees

m.viddya

the answer is 2..

RyuAmakusa

eistien The problem is you would not condition for maxima but it wiil be for minima