NZ Level 8 (NZC) Level 3 (NCEA) [In development]
Solve equations using trigonometric identities

## Interactive practice questions

Use the product-to-sum identities to express $2\cos\left(3x\right)\cos\left(9x\right)$2cos(3x)cos(9x) as a sum or difference of two trigonometric functions.

Easy
Approx 3 minutes

Express $\cos\left(3x+2y\right)\cos\left(x-y\right)$cos(3x+2y)cos(xy) as a sum or difference of two trigonometric functions.

Evaluate $\cos105^\circ\cos15^\circ$cos105°cos15° by first expressing it as a sum or difference of two trigonometric functions using the product-to-sum identities.

Express $2\sin\left(3x\right)\sin\left(4x\right)$2sin(3x)sin(4x) as a sum or difference of two trigonometric functions by using the product-to-sum identities.

### Outcomes

#### M8-6

Manipulate trigonometric expressions

#### 91575

Apply trigonometric methods in solving problems