Solve cos42^circcos18^circ-cos48^circcos72^circ

$$\cos 42 ^ { \circ } \cos 18 ^ { \circ } - \cos 48 ^ { \circ } \cos 72 ^ { \circ }$$

Evaluate

$$0.49999999999999990004969080200811$$

Solution Steps

Evaluate trigonometric functions in the problem

$$0.7431448254773942 \cdot 0.9510565162951535 - 0.6691306063588582 \cdot 0.30901699437494745$$

Multiply 0.7431448254773942 and 0.9510565162951535 to get 0.7067727288213003608571492690097.

$$0.7067727288213003608571492690097-0.6691306063588582\times 0.30901699437494745$$

Multiply 0.6691306063588582 and 0.30901699437494745 to get 0.20677272882130046080745846700159.

$$0.7067727288213003608571492690097-0.20677272882130046080745846700159$$

Subtract 0.20677272882130046080745846700159 from 0.7067727288213003608571492690097 to get 0.49999999999999990004969080200811.

$$0.49999999999999990004969080200811$$