Q. If x=2sinθ−sin2θ and y=2cosθ−cos2θ, θ∈[0,2π], then (d2y)/(dx2) at θ=π is :
Find Expressions for dxdy and dx2d2y: First, we need to find the expressions for dxdy and dx2d2y. To do this, we will differentiate x and y with respect to θ and then use the chain rule to find dxdy as dθdy divided by dθdx.
Differentiate x and y with respect to θ: Differentiate x with respect to θ: x=2sin(θ)−sin(2θ) dθdx=dθd[2sin(θ)−sin(2θ)] Using the chain rule and trigonometric identities, we get: dθdx=2cos(θ)−2cos(2θ)
Find dxdy by dividing dθdy by dθdx: Differentiate y with respect to θ: y=2cos(θ)−cos(2θ) dθdy=dθd[2cos(θ)−cos(2θ)] Using the chain rule and trigonometric identities, we get: dθdy=−2sin(θ)+2sin(2θ)
Differentiate dxdy with respect to θ: Now we find dxdy by dividing dθdy by dθdx: dxdy=dθdxdθdy dxdy=2cos(θ)−2cos(2θ)−2sin(θ)+2sin(2θ)
Apply Quotient Rule to find d2y/dx2: Next, we differentiate dy/dx with respect to θ to find d2y/dx2. This requires using the quotient rule:d2y/dx2=(dx/dθ)d/dθ[dy/dx]
Differentiate dθdy and dθdx with respect to θ: Apply the quotient rule:dx2d2y=(dθdx)2(dθdx)(dθd)(dθdy)−(dθdy)(dθd)(dθdx)
Evaluate expression at θ=π: We need to differentiate dθdy and dθdx with respect to θ: dθd(dθdy)=dθd(−2sin(θ)+2sin(2θ)) dθd(dθdx)=dθd(2cos(θ)−2cos(2θ))
Substitute values into expression: Differentiate both expressions:dθd(dθdy)=−2cos(θ)+4cos(2θ)dθd(dθdx)=−2sin(θ)+4sin(2θ)
Simplify the expression: Substitute these derivatives back into the expression for dx2d2y:dx2d2y=(2cos(θ)−2cos(2θ))2[(2cos(θ)−2cos(2θ))(−2cos(θ)+4cos(2θ))−(−2sin(θ)+2sin(2θ))(−2sin(θ)+4sin(2θ))]
Simplify the expression: Substitute these derivatives back into the expression for dx2d2y:dx2d2y=(2cos(θ)−2cos(2θ))2[(2cos(θ)−2cos(2θ))(−2cos(θ)+4cos(2θ))−(−2sin(θ)+2sin(2θ))(−2sin(θ)+4sin(2θ))]Now we need to evaluate this expression at θ=π:At θ=π, we have:sin(π)=0,sin(2π)=0cos(π)=−1,cos(2π)=1
Simplify the expression: Substitute these derivatives back into the expression for d2y/dx2:d2y/dx2=(2cos(θ)−2cos(2θ))2[(2cos(θ)−2cos(2θ))(−2cos(θ)+4cos(2θ))−(−2sin(θ)+2sin(2θ))(−2sin(θ)+4sin(2θ))]Now we need to evaluate this expression at θ=π:At θ=π, we have:sin(π)=0,sin(2π)=0cos(π)=−1,cos(2π)=1Substitute these values into the expression for d2y/dx2:d2y/dx2=(2(−1)−2(1))2[(2(−1)−2(1))(−2(−1)+4(1))−(−2(0)+2(0))(−2(0)+4(0))]
Simplify the expression: Substitute these derivatives back into the expression for d2y/dx2:d2y/dx2=(2cos(θ)−2cos(2θ))2[(2cos(θ)−2cos(2θ))(−2cos(θ)+4cos(2θ))−(−2sin(θ)+2sin(2θ))(−2sin(θ)+4sin(2θ))]Now we need to evaluate this expression at θ=π: At θ=π, we have:sin(π)=0,sin(2π)=0cos(π)=−1,cos(2π)=1Substitute these values into the expression for d2y/dx2:d2y/dx2=(2(−1)−2(1))2[(2(−1)−2(1))(−2(−1)+4(1))−(−2(0)+2(0))(−2(0)+4(0))]Simplify the expression:d2y/dx2=((−2−2)2)((−2−2)(2+4))d2y/dx2=(−4)2(−4)(6)d2y/dx2=16−24d2y/dx2=−23