In a ∆ABC, if show that its area is sq.units.

Note: In any ΔABC we define ‘a’ as length of side opposite to ∠A , ‘b’ as length of side opposite to ∠B and ‘c’ as length of side opposite to ∠C .

Key point to solve the problem:

• Area of ΔABC = 0.5(product of any two sides)×( sine of angle between them)

• Idea of cosine formula: Cos A =

Given

∴ Cos A =

∵ Area of ΔABC =

We need to find sin A

As we know that - sin²A = 1 – cos²A {using trigonometric identity}

∴ sin A =

∴ ar(ΔABC) = sq units. …ans