Question
The expression is equal to -
- cos2 A
- sin2 A
- cosA cosB cosC
- None of these
Hint:
simplify the expression by multiplying the terms and grouping the common terms. then apply the cosine property to reduce it to the required answer.
The correct answer is: sin2 A
sin2A
((b+c)2-a2)(a2-(b-c)2)/4b2c2
=((b2+c2-a2+2bc)/2bc)(( 2bc-( b2+c2-a2)/2bc)
=((2bc)2-( b2+c2-a2)2)/(2bc)2
in a triangle, cos A = (b2+c2-a2)/2bc
(4b2c2-4b2c2cosA)/4b2c2
= 1-cos2A= sin2A
In a triangle ABC, cos A = (b2+c2-a2)/2bc
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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.