sinē(1°)+sinē(2°)+···+sinē(88°)+sinē(89°) = Put some terms in the middle: sinē(1°)+sinē(2°)+···+sinē(44°)+sinē(45°)+sinē(46°)+···+sinē(88°)+sinē(89°) sinē(1°)+sinē(2°)+···+sinē(44°)+sinē(45°)+sinē(90°-44°)+···+sinē(90°-2°)+sinē(90°-1°) Use the fact that sin(90°-q) = cos(q) sinē(1°)+sinē(2°)+···+sinē(44°)+sinē(45°)+cosē(44°)+···+cosē(2°)+cosē(1°) = Rearrange the terms putting the 1st and 89th terms together, 2nd and 88th terms together, ··· 44th and 46th terms together: [sinē(1°)+cosē(1°)]+[sinē(2°)+cosē(2°)]+···+[sinē(44°)+cosē(44°)]+sinē(45°) = Use the fact that sinē(q)+cosē(q) = 1 1 + 1 + ··· + 1 + sinē(45°), where there are 44 1's. 44 + sinē(45°) = 44 += 44 + = 44 + = 44.5 Edwin