Solve 2cos(40^circ)cos(80^circ)+cos(140^circ)

$$2 \cos ( 40 ^ { \circ } ) \cos ( 80 ^ { \circ } ) + \cos ( 140 ^ { \circ } )$$

Evaluate

$$-0.49999999999999978333866464735804$$

Solution Steps

Evaluate trigonometric functions in the problem

$$2 \cdot 0.766044443118978 \cdot 0.17364817766693041 + -0.7660444431189779$$

Multiply 2 and 0.766044443118978 to get 1.532088886237956.

$$1.532088886237956\times 0.17364817766693041-0.7660444431189779$$

Multiply 1.532088886237956 and 0.17364817766693041 to get 0.26604444311897811666133535264196.

$$0.26604444311897811666133535264196-0.7660444431189779$$

Subtract 0.7660444431189779 from 0.26604444311897811666133535264196 to get -0.49999999999999978333866464735804.

$$-0.49999999999999978333866464735804$$