Option 3 : \(\dfrac{4}{5}\)

**GIVEN:**

sin A = 3/5

**FORMULAE USED:**

sin θ = Perpendicular/hypotenuse

cos θ = Base/hypotenuse

**CALCULATION:**

Perpendicular = 3X

Hypotenuse = 5X

using pythagoras theorem

hypotenuse^{2} = Perpendicular^{2} + Base^{2}

(5X)^{2} = (3X)^{2} + Base^{2}

Base^{2} = (25 - 9)X^{2} = 16X^{2}

Base = 4x

cos A = 4X/5X

∴ cos A = 4/5

We know that,

Sin^{2}θ + Cos^{2}θ = 1

⇒ Cosθ = √(1 - Sin^{2}θ)

SinA = 3/5

⇒ CosA = √{1 - (3/5)^{2}}

⇒ CosA = √{(25 - 9)/25} = 4/5