sin(-420°)= -0.866025
cos(-750°)= 0.866025
tg(-405°)= -1
2cos60°-tg π/4= 0.986292
ctg45°-2sin π/6= 1.98172
2cos30°·ctg60°-sin 3π/2= 2.91784
ctg405°-ctg(-405°)÷2sin(-750°)= 0.75
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