someone please let me know, why

become

where to get the formulae

they should have givn you a list of "reference" angles for 0, pi/6, pi/4, pi/3, pi/2

you can see it here: http://www.purplemath.com/modules/trig.htm

they just plugged the numbers in like sin pi/4 = sqrt2 / 2 you just memorize it

you can see it here: http://www.purplemath.com/modules/trig.htm

they just plugged the numbers in like sin pi/4 = sqrt2 / 2 you just memorize it