Final: Two Angles

Part of the Trig Identities section of Coddy's Trigonometry journey. Lesson 43 of 48.

Prove the identity in the prompt. Two different angles appear, x and y.

Challenge

Prove that $\frac{\cos\left(x+y\right)+\sin\left(x\right)\sin\left(y\right)}{\cos\left(x\right)}$ equals $\cos\left(y\right)$ : rewrite it until the board reads $\cos\left(y\right)$ . Then press Check.

Try it yourself

\frac{\cos\left(x+y\right)+\sin x \sin y}{\cos x}

Rewrite as $\cos y$

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Trig Identities

1Identities on the Circle

sin²x + cos²x = 1 Squares Erase the Signs Recap: the Circle Identity

4Even, Odd and Cofunctions

Negative Angles Even and Odd in a Proof Even and Odd Graphs Cofunctions Recap: Signs of Angles

7Double-Angle Formulas

sin 2x = 2 sin x cos x Three Forms of cos 2x Exact Values, Doubled Square, Then Double The Graph of 2 sin x cos x Recap: Double Angles

10Final Challenges

Final: Two AnglesFinal: Tangents to sin 2x Final: An Exact Product Final: A Wave in Disguise Final: Two Squares Final: Choose the Form

2Reciprocal and Quotient

Identity or Equation?Secant, Cosecant, Cotangent Recap: Reciprocals

5Proving Identities

Work on One Side Rewrite in sin and cos Factor First Make One Fraction Proofs That Go Wrong Recap: Prove It

8Half Angles, Power Reduction

Power Reduction sin²x Is a Wave Half-Angle Values tan of a Half Angle Recap: Half Angles

3Pythagorean Identities

1 + tan²x = sec²x A Difference of Squares Squaring a Sum Recap: Three Forms

6Sum and Difference

sin(A + B) and sin(A - B)cos(A + B) and cos(A - B)Turning by 90° and 180°Read the Formula Backwards tan(A + B) and tan(A - B)Recap: Sum Formulas

9Product to Sum

Products to Sums Sums to Products Sums Over Sums Recap: Sum to Product