The problem is to simplify the expression $M = (sin\theta - cos\theta)^2 + 2sin^2\theta + cot\theta$.

AlgebraTrigonometryTrigonometric IdentitiesSimplificationDouble Angle Formulas
2025/5/25

1. Problem Description

The problem is to simplify the expression M=(sinθcosθ)2+2sin2θ+cotθM = (sin\theta - cos\theta)^2 + 2sin^2\theta + cot\theta.

2. Solution Steps

First, expand the square:
(sinθcosθ)2=sin2θ2sinθcosθ+cos2θ(sin\theta - cos\theta)^2 = sin^2\theta - 2sin\theta cos\theta + cos^2\theta
Substitute this back into the expression for M:
M=sin2θ2sinθcosθ+cos2θ+2sin2θ+cotθM = sin^2\theta - 2sin\theta cos\theta + cos^2\theta + 2sin^2\theta + cot\theta
Rearrange the terms:
M=sin2θ+cos2θ+2sin2θ2sinθcosθ+cotθM = sin^2\theta + cos^2\theta + 2sin^2\theta - 2sin\theta cos\theta + cot\theta
Use the identity sin2θ+cos2θ=1sin^2\theta + cos^2\theta = 1:
M=1+2sin2θ2sinθcosθ+cotθM = 1 + 2sin^2\theta - 2sin\theta cos\theta + cot\theta
Rewrite cotθcot\theta as cosθsinθ\frac{cos\theta}{sin\theta}:
M=1+2sin2θ2sinθcosθ+cosθsinθM = 1 + 2sin^2\theta - 2sin\theta cos\theta + \frac{cos\theta}{sin\theta}
Combine the last two terms:
M=1+2sin2θ+cosθ2sin2θcosθsinθM = 1 + 2sin^2\theta + \frac{cos\theta - 2sin^2\theta cos\theta}{sin\theta}
Factor cosθcos\theta from the numerator:
M=1+2sin2θ+cosθ(12sin2θ)sinθM = 1 + 2sin^2\theta + \frac{cos\theta (1 - 2sin^2\theta)}{sin\theta}
Use the double angle formula cos(2θ)=12sin2θcos(2\theta) = 1 - 2sin^2\theta:
M=1+2sin2θ+cosθcos(2θ)sinθM = 1 + 2sin^2\theta + \frac{cos\theta cos(2\theta)}{sin\theta}
M=1+2sin2θ+cotθcos(2θ)M = 1 + 2sin^2\theta + cot\theta cos(2\theta)
However, let's retrace our steps from the earlier equation:
M=1+2sin2θ2sinθcosθ+cotθM = 1 + 2sin^2\theta - 2sin\theta cos\theta + cot\theta
M=1+2sin2θsin(2θ)+cotθM = 1 + 2sin^2\theta - sin(2\theta) + cot\theta
Also consider
M=sin2θ2sinθcosθ+cos2θ+2sin2θ+cosθsinθM = sin^2\theta - 2sin\theta cos\theta + cos^2\theta + 2sin^2\theta + \frac{cos\theta}{sin\theta}
M=3sin2θ2sinθcosθ+cos2θ+cosθsinθM = 3sin^2\theta - 2sin\theta cos\theta + cos^2\theta + \frac{cos\theta}{sin\theta}
M=3sin2θsin(2θ)+cos2θ+cosθsinθM = 3sin^2\theta - sin(2\theta) + cos^2\theta + \frac{cos\theta}{sin\theta}
M=2sin2θsin(2θ)+sin2θ+cos2θ+cosθsinθM = 2sin^2\theta - sin(2\theta) + sin^2\theta + cos^2\theta + \frac{cos\theta}{sin\theta}
M=2sin2θsin(2θ)+1+cosθsinθM = 2sin^2\theta - sin(2\theta) + 1 + \frac{cos\theta}{sin\theta}
M=2sin2θsin(2θ)+1+cotθM = 2sin^2\theta - sin(2\theta) + 1 + cot\theta
M=1sin(2θ)+cotθ+2sin2θM = 1 - sin(2\theta) + cot\theta + 2sin^2\theta
Let's go back to
M=1+2sin2θ2sinθcosθ+cotθM = 1 + 2sin^2\theta - 2sin\theta cos\theta + cot\theta
M=1+2sin2θsin2θ+cotθM = 1 + 2sin^2\theta - sin2\theta + cot\theta
Let's try M=1+2sin2θsin2θ+cosθsinθ=1+2sin2θsin2θ+cotθM = 1 + 2sin^2\theta - sin2\theta + \frac{cos\theta}{sin\theta} = 1 + 2sin^2\theta - sin2\theta + cot\theta

3. Final Answer

M=1+2sin2θsin(2θ)+cotθM = 1 + 2sin^2\theta - sin(2\theta) + cot\theta

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