Rewrite the given expression as
3sin (2π/3) − 4cos (5π/2).
For one accustomed to measure in Degrees,
(π/3) and (π/2) Radians are more familiar as 60° and 90°.
Next, 3sin (2π/3) − 4cos (5π/2) translates to
3sin (2 × 60°) − 4cos (5 × 90°) or
3sin (120°) − 4cos (450°) or
3sin (180° − 120°) − 4cos (450° − 360°).
Then 3sin (60°) − 4cos (90°) with knowledge
of Trigonometry goes to 3×(√3/2) − 4×(0).
A calculator reduces this last to 2.598076211
(equal to the square root of 6.749999999999
or √6.75).
