I WANT TO SOLVE THIS TRIANGLE

Level pending

If the area of a triangle ABC is 2 square units, then the value of (c^{2}sin2B + b^{2}sin2C) is equal to what? [NOTE: All symbols used have usual meanings in triangle ABC]


The answer is 8.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Washeef Mohammad
Dec 25, 2013

A little tricky idea can solve it amaizingly. Since the area of the triangle is 2 sqaure units, so let's assume the A = 9 0 \angle A = 90 ^ \circ and b = c = 2 b=c=2 [ so that the area is 1 2 × 2 × 2 = 2 \frac{1}{2} \times 2 \times 2 = 2 ].

Now, since we assumed b = c = 2 b=c=2

Therefore, B = C = 4 5 \angle B = \angle C= 45^ \circ

c 2 s i n 2 B + b 2 s i n 2 C = 2 b 2 sin ( 2 B ) = 2 × 2 2 × 1 = 8 \Rightarrow c^{2}sin2B + b^{2}sin2C= 2b^{2}\sin (2B) =2 \times 2^{2} \times1= 8

Infinity Moon
Dec 22, 2013

area of triangle=2(square units);

c^2 sin2B + b^2 Sin2C=?

tools-

sin(x+y)=sinxcosy+cosxsiny

a/SinA = b/SinB=c/SinC

=) SinC=c SinB/b

=) SinB=bSinC/c

Sin2B=2sinBcosB

sin2C=2SinCcosC

now the solving part

c^2 Sin2B +b^2Sin2C

=c^2 (2sinBcosB) + b^2 (2SinCcosC)

=2(c^2(bSinCcosB/c) + b^2 (c SinBcosC/b))

=2cb(sinCcosB+sinBcosC)

=2cbSin(C+B)--------(Sin (C+B)=Sin (180-(c+b))=Sin(A)

=2cbSinA----eq 1

Area of the triangle = bcSinA/2 =2

=) bcSinA=4

so value of eq 1= 4*2 = 8

i did it in this way good solution

Priyesh Pandey - 7 years, 5 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...