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Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) §1.5 A Review of Trigonometry, #29 · Trigonometry · Identities

Rewrite … as … by choosing the correct “phase angle”

Rewrite $cos θ + sin θ$ as $2 sin (θ + ϕ)$ by choosing the correct “phase angle” $ϕ$ . (Make the equation correct at $θ = 0$ . Square both sides to check.)

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Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §1.5 A Review of Trigonometry, #29

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