Question
If in a ΔABC, (sin A + sin B + sin C)(sin A + sin B – sin C)= 3 sin A sin B, then –
- A = 60°
- B = 60°
- C = 60°
- None of these
Hint:
use the sine rule to replace the sin angle terms with side lengths and simplify .
The correct answer is: C = 60°
c=60 degree
we know that
a/sin A =b/sin B = c/sinC = 2R
(sine rule)
Therefore, we can replace sinA, sin B and sinC as follows:
(a/2R+b/2R+c/2R)( a/2R+b/2R-c/2R)=3x a/2Rx b/2R
=> (a+b+c)(a+b+c)=3ab
Or
a2+b2+2ab -c2=3ab
a2+b2+-c2=ab
we know that
cos C = (a2+b2-c2)/2ab
=ab/2ab = ½
C = cos-1(1/2)= 60 degree
the sine rule states that
a/sin A =b/sin B = c/sinC = 2R
this is used to find the relation of the angles and sides of the triangles.
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Statement- (1) : The tangents drawn to the parabola y2 = 4ax at the ends of any focal chord intersect on the directrix.
Statement- (2) : The point of intersection of the tangents at drawn at P(t1) and Q(t2) are the parabola y2 = 4ax is {at1t2, a(t1 + t2)}
Statement- (1) : The tangents drawn to the parabola y2 = 4ax at the ends of any focal chord intersect on the directrix.
Statement- (2) : The point of intersection of the tangents at drawn at P(t1) and Q(t2) are the parabola y2 = 4ax is {at1t2, a(t1 + t2)}
Statement- (1) : PQ is a focal chord of a parabola. Then the tangent at P to the parabola is parallel to the normal at Q.
Statement- (2) : If P(t1) and Q(t2) are the ends of a focal chord of the parabola y2 = 4ax, then t1t2 = –1.
slopes at the two extremeties of a focal chord are : (t,-1/t)
this property is used to explain the behaviour of tangents and normals at the respective points.
Statement- (1) : PQ is a focal chord of a parabola. Then the tangent at P to the parabola is parallel to the normal at Q.
Statement- (2) : If P(t1) and Q(t2) are the ends of a focal chord of the parabola y2 = 4ax, then t1t2 = –1.
slopes at the two extremeties of a focal chord are : (t,-1/t)
this property is used to explain the behaviour of tangents and normals at the respective points.